I know Coolwater gets a lot of hate, but ironically its the only frag I have that had random people saying “what smells so good” when they walked by me.Sounds like she might have something specific in mind. Why not ask her, or if you have asked her, what did she say exactly except for "clean smelling." It is hard to guess at someone else might like in a frag.
The fact that she does not like Aventus is throwing me, too. It is not my favorite frag, but my sense would have been that it was nearly universally popular among younger folks. Actually, just how young are we talking? How old are you? Maybe she is thinking something like Le Male or Sauvage. I guess I would put Bleu de Chanel in there, too. Those are scents of a particular type to me, which I suppose someone might describe as clean smelling, even if I would not necessarily do so, that have been hugely popular in, say, the recent decade. To me the have been somewhat overplayed, and to wear them might risk seeming out of date.
And, no, I would not think Cool Water.
A trip to the local frag shop with her might well be in order, but I personally find it difficult to pick out frags to actually buy based on sampling them at a fragrance counter. The way they evolve after being applied for some time is more important than fleeting top notes, and that is hard to judge for multiple scents at a time.
Check out You Tube maybe for what might be currently popular among younger people that is described as clean smelling.