Had a 3-4 day vacation with someone before in the relatively early dating stages.
Her idea. I was already going on the trip for ~2.5 weeks, and she wanted to tag along for a portion of it.
Turns out she implicitly took this to mean that we were much more committed now, and when I didn't put in "a lot of extra effort" afterwards, she got resentful over it.
Things were already going downhill with her anyways, left out a lot of details & context here, though the dynamic that unfolded post-vacation probably didn't help the situation.
Point being, I second DW3's advice here:
It’s relationship territory for sure. If she doesn’t have strong feelings for you now, she will after the trip. You’re giving her a clear indication of your interest in her as a potential partner in doing this. If that’s what you want, you should definitely go for it. It’ll be a lot of fun in that regard.
If you think that it’s not that level, then consequently by taking the trip you’re going to entwine yourself in a way where it gets more tense when you’re not giving her the time she’s expecting after that trip. I just spent the weekend at a wedding with my girlfriend and she thought I was going to see her today as well. When she called me a few minutes ago, and I told her that I was going to probably stick around here and had things to do, you could hear that little brat inside come out and she actually ended the call in under 5 minutes which is totally out of character.
She also made a big deal of relatively minor things, minor incompatibilities:
Nothing will bring incompatibilities into focus more than travelling together, you'll either hit it off great or you'll start to hate each other.