will or would?

Which one is grammatically correct?

Even if I do invite her, she (won't, wouldn't) accept my invitation.

won't

But what if the sentence goes like that:

Even if I WILL invite her, she (won't, wouldn't) accept my invitation.

Wouldn't you have to use wouldn't here?

Why?

I think both "won't" and "wouldn't" are possible in these sentences.

"Won't" sounds a bit more definite or known, and "wouldn't" a bit more conditional or assumed. In any case, I wouldn't say either of them is really "gramatically incorrect".

Both. Wouldn't and will are different.

wouldn't (might)
will (she is for sure)