What should i do? my friend order drinks and i end up pay more for our bill !!?

I think you're right in asking for separate bills. Just make that clear at the very beginning so that she doesn't think that you'll pay for her again. Also you can just tell the bartender or server that you want separate bills before you order. I know its a tough and very awkward situation but you have to be firm. Just let her know that you really enjoy her company but can't keep paying and that if this is something she cannot afford, you guys can meet up somewhere else and do some free stuff like watching a rented movie where one pays for the movie and other for snacks. To answer her when she says that she paid for yours, tell her that you really did appreciate that and thats why you paid for the last three times.

A good idea have your own bill, and say no when she gets the drinks and tell to pay for them herself

Separating your bills is the best idea, it's not fair that she does that to you, If she doesn't have the money to pay for expensive drinks then she shouldn't order them. If she's nOt embarrassed to over order and pin it on you then you shouldn't feel embarrassed about separating orders, what you should do is not even tell her just tell the bartender or waitress to give separate bills and if she says anything to u just tell her "what's wrong with each one of us coverEring our bills?" if she says she doesn't have any money then ask why she bothered to go out?

never think more or less ... all that in friendship