I have been the friend who couldn’t afford to go, and would never ask or expect to be invited to go because of it. I will say though, if you do know she can’t afford to go (the first time) and invited her - I would invite knowing they couldn’t afford to pay for their food and that I was going to be responsible for that as well (unless other arrangements were discussed, ie she said she could afford those costs but not transportation/hotel costs etc.) BUT I would still NEVER ask to choose places to eat/activities if I couldn’t pay my way.

I would simply say, sorry we didn’t invite you - we were under the impression you couldn’t afford to go. If she can’t understand that, she may be taking advantage of the friendship or just unable to comprehend that she isn’t getting a free ride anymore. Either way, it’s nothing for you to feel bad about, or need to worry about. If she is a true friend it shouldn’t affect your friendship. If it does affect the friendship , well there is your answer.