If you're sure one is a girl and one is a boy you should be fine. If both are boys, they won't get along for long if at all. Some females are just not friendly to anyone else, so watch for that.

As far as over breeding, if she's well fed and able, she'll produce eggs and one breeding is all it takes for the season, so I wouldn't worry about that. Make sure she's got calcium in her supplement.

Also check out www.leopardgeckoforums.net

It's pretty much THE place for geckos.