I would guess any opener that would give you a strong reason to contact her that doesn't have to do with her. That would be the safest. Ex: If you had stuff to pick up or drop off.
Of you can cut to the chase and ask her how her trip was. Mind you this is a bit riskier.
I also think two weeks isn't enough. Especially if she is coming back from a kind of "vacation" which, to her, would be over in the blink of an eye. So she may not have been reflecting on your relationship as much as you might think. Best let her contact you in a few weeks after she gets back, but that's my opinion.