I'm smart with my money (I think, anyways), so I could spend that money on it. It really doesn't have to do with not being able to afford it. It has to do with the fact that I think it's rude to ask me to spend that much, whether you know I can afford it or not, when you know about all the other shit I need to buy for your wedding.
And for the people saying it doesn't sound like I like her much, I do. We're not best friends, but we hang out a lot. She's not some completely random acquaintance. I just don't like this act specifically.