I think you should just level with her, tell her the information behind corals and plants in a tank, discuss the possibility of later contamination and the fact that they don't look real good in tanks, and you'll probably be constantly fussing with them to get them to stay put, etc.
She should want to do whatever is best in the longrun of the fish - and if it's a certain look she wants, can you see if you can find something that might look more like a seaweed plant?
Anyway, girlfriend or not, the health of the fish come first, IMO. Who's tank is it, anyway? Who's spending the money on it?
Can you compromise, say, if you pick the decor, she picks most of the fish? etc.
She should want to do whatever is best in the longrun of the fish - and if it's a certain look she wants, can you see if you can find something that might look more like a seaweed plant?
Anyway, girlfriend or not, the health of the fish come first, IMO. Who's tank is it, anyway? Who's spending the money on it?
Can you compromise, say, if you pick the decor, she picks most of the fish? etc.