Take a hint, she doesn't want to write with you. Saying no should be enough for you to back off, you should value your friends choice over anonymous strangers and then shut up about her choice
I'm sorry, but having a half hearted companion in your writing isn't going to help your writing, and it will waste their time which could be spent on stuff they want to do.
If she dosn't want to, then do not try to make her.
If she does help you, be on the lookout for work that's so okay it's average.