It's not crass at all, many couples are living together before they get married these days and so don't need a gift list in it's traditional sense. Some views on here are out dated and old fashioned.
Whenever we've given money we have often done it as a friendship group, could you club together with other friends going to the wedding? The other thing you could do is once the honeymoon is booked is gift them vouchers for an experience while they are away, I bought a champagne afternoon tea for my friend and her husband while they were touring Scotland and in Edinburgh.
If those aren't possibilities, just because she has asked for money, it doesn't mean you have to do that, just buy a nice gift anyway.
Don't feel you have to spend a lot, these events do put unnecessary pressure on, spend what you can afford, we all have a snobby friends but you shouldn't be judged.