FSIL's engagement party ...

is next friday night and I have a question. She is my MOH and for our engagement party they gave us $300.00, (her FH is also in our wedding party) and we are both in their wedding party as well. Should I give them what they gave us or should I get them something for that price off their registry? The thing is they really don't need the $ for the wedding so maybe a gift is more practical. Or should I just give them $? Don't know what to do..what would all of you do? Personally I would rather $ because she still has her shower ..right?
Confused.. please help!!!

if they dont need money,
maybe do a split gift? something off their registry(maybe something they could start using now)and money for the rest...

I think either is fine. In a roundabout way get her into a conversation about what's on her registry. If she goes on about certain things like how much she loves her china or wine glasses or whatever, get her that. Money is fine too, I doubt they'll mind.