Bad dreams seem pretty common amongst kids. When DS was little, it helped for me to cuddle him and talk through his day with him (daycare wrote out what he did there, so I would just talk through getting up, all the thing he'd done at home, then travel to daycare, etc.) and that helped 'cap' the day. He would correct me and got more involved as his vocabulary grew. Its great practise for LO to get used to talking through their day (you are setting up a way to get info about what happens at school...) for later when you've less of an idea about what's happening too. I cannot say that stopped the dreams but reduced them for sure.
FWIW, the dream can be as simple as processing that moment that you walked out of the room for a moment or that time you said 'no' to something. Everything in the world is so new, she's not able to justify those experiences like we can. That doesn't mean you spend your entire time stopping her from ever having a perceived negative experience, just that you help her feel safe and loved in those moments and this too shall pass, just probably not in a few weeks, sadly.