Plus the point you raised was quite valid.
Just as a general guideline or rule of thumb:
You're not going to get in her pants by going Dutch.
That's not a set in stone law but it's a good guideline. A fair trade off is at least when it comes to paying the dinner check is always always always get it the first time and if she offers to pay politely decline. If she insists, offer her the chance to pay next time. That's legit.
In the case of cost sharing on a flight you're doing anyway, politely decline her offer to pay if she makes it. You're in an airplane so you need to hold yourself to that higher standard, man up and be a baller.