You seem to think that she's younger than she's supposed to be, so maybe she's not able to digest her food properly. And she shouldn't be fed cow's milk, that can often cause upset tums in cats. Did she use a wormer suitable for such a young kitten?
If not, it may have been too strong. Or it could be an infection - or any one of a number of things. A dose of antibiotics may be in order.
As she's so small, she needs to have a litter tray with low sides rather than the normal size one. A disposable foil baking tray, maybe, or just some litter on newspaper on plastic, so she doesn't have to scale a wall to use it. Plus if her bottom's hurting her, she may associate the tray with being hurt and so be avoiding it.
You mention another kitten - is it using the same litter tray? Some cats won't use one that other cats are using. She could try putting her in another room with some fresh litter of her own and see if that helps, but it's not going to help her diarrhoea.
You know the only real answer is a visit to the vet, that's the only way anyone's going to diagnose the problem. I'm with you, you shouldn't have animals if you're not prepared to take them to the vet when they need it. Would she let you take her?
Maybe that would be the best solution. I hope so, because you seem to care about the kitty much more than she does. If my husband told me I couldn't take a kitten to the vet (not that he would) he'd be in big trouble!
The kitten is far to young to be dewormed with over the counter flea medication - it can be quite toxic to an adult cat, let alone a tiny kitten. It's going poo all over because it has the diarrhea! And a small kitten with diarrhea will quickly dehydrate and die.
Kittens are NOT reliably litter trained until around10 weeks, so no matter how many times she puts her in the box, she's too young to "hold it" long, and she will go elsewhere. The kitten needs to go to the vet, like it or not. She's given her an inappropriate medication which has cause diarrhea - the kitten as I said is going to dehydrate and die.
No advice other than to tell your friend to suck it up and get her seen by the vet, and to NEVER self medicate kittens (or cats) with guesses on drugs from the store.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.