It’s not as if her daughter had nowhere to go. She had two adults at home who were ready and willing to take care of her for the duration of the trip! 

«Who should I take on vacation with me?» can be a difficult question to answer. You’re going to have a very different experience in London if you go with your parents than if you go with friends your own age. If you’re single, you might not want to go on vacation with six couples who don’t know how to hang out with their friends when their partner is in the same room. If you have a boyfriend of four years, it’d be kind of strange if you wanted to go on a six-week-long European vacation by yourself. Who you choose to go on vacation with is just as important as the location you visit and where you choose to lodge. It’s perfectly reasonable to be pretty exclusive about who you travel with. I would get angry if someone invited a really annoying person to my excursion to Fire Island without asking the group if it was okay to invite them, and that doesn’t make me a mean girl.