I read this maybe fifteen years ago but got the impression it was a few years older (well thumbed in an English library).
Plot details I remember:
She lives on another planet (or parallel dimension) and is part of a team who somehow teleport to Earth to do surveys and such.
Her people have bred for genetic perfection for so long that the women are all knock out and the men are like Mr Swoon types. Sadly she never lucked out in this good looks thing, so although on our world she is like the hottest babe ever, back on her own world she is an object of pity.
On the other world there is some back story about a conflict but details escape me.
Back on Earth our male has some kind of Stephen Hawkins type issues and is in a wheelchair. He ends up with some friends on a country day out but (can't recall how) he gets separated. He rolls into a forest clearing and espies "the most beautiful girl ever"
She looks alarmed, waves her hand about while muttering, and disappears.
Being a brainiac he realises what he has just witnessed and the implications of other world contact, he noted she moved her finger in a graceful arc and that means maths. Back at university he specialises in exotic mathematics and gradually becomes an expert.
On the alien world the conflict and power intrigues deepen and the girl returns to Earth looking for an edge. She learns of this genius and makes contact, recognition on both sides. She takes him to her world where his looks revolt the perfect people but his brain impresses them.
Somehow he helps them to prevail (I think this also helps our Earth's survival in a hostile galaxy) and becomes a hero to them. I want to say they end up as a couple with homes on both worlds but am a bit unsure on that. Also I can't recall if the Earth setting was America or England.
All memories drained now, I'm out.