This sounds like no risk to me. If her genital area did not touch yours directly, there was no 'skin to skin' contact. That doesn't mean skin to g string thong contact but genital to genital. This didn't happen, I'd not be concerned. Covered oral sex is also such that you were safe. I'd not be concerned about std's.
I agree with GuitarRox. I wouldn't worry about this at all.