I don't think I would try to influence her this way.I think willingly wearers could accept it if they think good things are more important than bad things(for example,they may want to stay virgin until marriage but think they would not be able to keep it when they would have a serious boyfriend).
Does your parents influenced you(and your older sister)this way?
I don't think it is something we can be proud(it is normal things),but I don't think it is better if avoided either.