If you do not attend the shower then you are not obligated to give a gift.
If you do not attend the wedding then you are not obligated to give a gift.
If you do attend either one, then give a gift from her registry that is within your budget or something that you pick out yourself that you can afford.
You are not obligated to spend beyond what you can afford regardless of what she has dictated.
But from what I've read in these posts, I wouldn't give her the time of day!