Nope, you can get Bella on the DIK path provided you don't beat up Troy and don't do anything with Cathy in Bella's car as Bella will find Cathy's panties in the car, other than that I don't think there are any other blocks block on Bella that isn't your choice.
But I'll agree about Nicole, not Lily, Nicole is probably the best relationship you can have, except maybe Zoey, as all the others have way too much baggage, Nicole's only baggage is a kid and that's not really a problem.
But you can only have a threesome with Sage and Quinn if you're on the DIK route and that makes it all worthwhile.