Well, I would start preparing your dog for the baby now by requiring that your dog do a Nothing In Life is Free program. Ie, if your dog wants attention, don't give it until you ask your dog to do something like sit and then call your dog over. If your dog wants food, same thing.
Wants to play, wants to go out, anything. This will help your dog because she will realize that she can't have what she wants when she wants it but when you will give it to her. It will also teach her to calm down and listen to you if she wants something.
Also, make sure you don't just let her force her attention on you. So, if you have someone sitting by you on the couch and she climbs up, then both of you stand up so that she can't cuddle and walk away from her or sit somewhere else. Do not allow her onto the couch with you unless you ask her to do something first and then invite her up onto the couch.
Do not allow her to snuggle up on you until you ask her to come up there. This is just basically teaching her that you say when the snuggles happen, not limiting snuggles, just taking control of when they happen. She also will be helped by regular exercise.
Since she came from a situation that might have made her nervous walking outside, walking her outside if she's stressed is not a good solution for exercise for her. If she likes walks, that's great! If she doesn't, then play fetch in the house or in the backyard where she feels safe.
You might also want to look into things she can do on her own, and baby gates to restrict her to a certain part of the house (for instance, keeping her out of the baby-room, or putting her in the bathroom while you're cooking dinner, etc.) Just things to make it so that if you were watching your new baby and you needed her out of the way she would have a visible structure that she would be behind, and not freak out at being separated from you. You need to start now on teaching her that being separated is alright so that it's not connected to the baby. Then you're going to want to get a baby-carrier or baby-car-seat or stroller and start pretending to have the baby and teaching the dog to sit while you do things like load, unload, feed, swaddle, etc the baby.
Also I would get a diaper pail and start doing things like putting something yummy smelling inside and making it dog-proof (because... well... better now than when you've got the baby.) Last... I would make sure she's not on a strict schedule. If you feed her at 7pm every night, stop. Feed her instead between 6pm-8pm and earlier say 11am-1pm.
This will help her be a bit more flexible if the baby causes disruptions. Ie, if you can't get her food to her at 7pm, she'll still be relaxed because you will probably get it before 8pm, and if you don't she has a meal in the morning too, so it's not a scary situation for the dog. If she's not flexible with her meals then if you're late with a meal it can cause meal-stress, and anxiety, and possibly a snappy behavior towards the baby who caused it.
Dogs just shouldn't be on a strict schedule. Keep it fairly loose so they can handle it if you're late or early some time. Really there's no reason to panic.
You've got months to work on this, and your dog is over 4 years old which is a great age to train new tricks to because they're past the 'young brainless' stage and your dog sounds very much like she'd do anything to be with people and snuggle up. I mean, she acts jealous... no, she acts like she wants to cuddle with everyone and to be the center of attention. Jealous dogs that I'd worry about are the ones who would growl at the person sitting by you, bite them, start barking, snarl, show teeth, or start doing anything to get you to get away from them.
Not the ones who want to snuggle up between you and the other person. Since she's female, she's older, and she loves people so much I'd be more concerned with her wanting to mother the baby than anything. Teaching her that you've got it under control, that you're the person she should look to rather than feel like she has to be responsible for anything, will help her relax when the baby comes.
Just like with every dog though you don't leave them alone with a baby. That's just basic safety. But if you start now just teaching her basic manners, basic NILIF, and helping her accept any rules that would be in place when the baby comes, then it should be fine.
One more thing. I recommend starting now because if you start changing patterns of behavior once the baby comes in a way that upsets her she will connect that to the baby. Ie, let's say you always walk her every day at 5pm.
Now the baby comes and you miss every other day. She will connect it to the baby and that's a negative with the baby. You want as many positives with the baby as possible.
(For instance, when you are feeding the baby it wouldn't hurt for your partner to feed your dog, and when your baby is older it wouldn't hurt for your baby to give treats to your dog with your supervision. Every positive you can give the two of them together the better it is.) Add: I would avoid any of the Dog Whisperer's advice. According to the American Veterinary Society of Animal Behavior the risk of having an aggressive reaction from a dog increases depending on the aggressiveness of the training methods.
For instance, if you force a dog on it's side around a baby when the dog is not comfortable with a baby to show that the baby has strength over the dog the dog is more likely to see a negative experience with the baby, and when the baby is alone decide to pin the baby down himself to prove that the baby cannot pin him. Or just will snap at the baby sometime when the baby just grabs him for fun. What we told people was that if the weakest member of your family cannot do the technique then you should not use that technique because the dog will recognize that person can't do it.
They don't generalize that a child is actually a part of the adult who can control them. Studies show that dogs don't think like that. Millan is very mistaken and in homes where children are involved it's not a good method to consider.
Add: Heh. My dog is about 35lbs a pure mix we got from a puppy-mill raid in New Mexico from a shelter. :) He doesn't like many people... puppy mills tend to cause problems with that.
But he LOVES our 2 year old, they play, she can grab and yank on him (though we are teaching her not to and do our best to help her stop) and he will not nip her. I love watching them play. He can get away anytime he wants to, but just loves it.
Oh... he's 35lbs and a lap dog, when invited up. :P He likes to snuggle in laps. And I don't mind it, so long as I asked.
It would have been hard to nurse her or feed her or anything if he had thought he could just climb up whenever he wanted.
Just from things I have read, and it goes for cats too, if the dog is jealous as you say, I would really watch the dog near the baby, don't leave the dog in the room with the baby alone because dogs act out in jealousy. I know with cats, it is said that they will try to smother babies over jealousy...so just be very cautious of the dog around the baby and see how it goes, you may be surprised, the dog may get a nurturing feel for the baby and you'll have no problems.