Note that I did actually like the show/character until S3, so I'm just starting from there:
1. Getting back together with Tom was stupid because it happened mostly offscreen, immediately after an entire episode showing she still has feelings for Marco. Just makes any shipping stuff with her suddenly feel much more shallow than it did before, because she seems completely cool with being with Tom even as he no longer seems into her.
2. Making Marco her squire was a shitty move for someone who's supposedly her best friend, because now he's working for her and she literally gives him orders.
3. She also says she supposedly did it just so the two of them can still have fun together and it's not meant to be that serious. Which feels hypocritical when she still gives him orders, and also shitty to the actual squires and knights by inserting herself and Marco in with them when they're taking it seriously.
4. Even though I'm sure it's going to be presented as a good thing, giving the wand and kingdom to Eclipsa is just so fucking stupid when in-universe she doesn't know shit about Eclipsa except "she was in love." And even then she has no way of knowing that for sure. The audience has been given a narrative so far of Eclipsa being apparently perfect and at this rate I doubt they're gonna take that back, so while it seems unlikely Star will be proven wrong it narratively almost feels like she should be.