I can't tell if this is a serious post or a light-hearted, joking post, but I'll give you a serious answer:
"Fair" doesn't really work in relationships. On the surface, sure, if she goes on a girls trip, it's only fair that you get to go on a boys trip, or a solo trip. However, in practice it's much more complicated. If Mr. CBs went off to WDW on his own, I'd feel sad and left out, even if it was "fair" because I'd gone somewhere else with a friend. I think I'd end up feeling as if I had to pay for my trip by agreeing to be excluded from his trip, and that would feel pretty terrible.
Your mileage may vary, but you're probably better off coming up with a plan that she's all for in the same way that you're all for her girls trip, rather than something you have to talk her into. Make it something she's genuinely happy to see you go off and do without her, not something she endures as payment for having done something fun without you. In other words, aim for emotional fairness, not simple quid pro quo.