Older Rat, Possible Malocculion? Worried about the sedation at the vet

So my baby is almost three years old now, and we booked an appointment for tomorrow at the vet for a possible malocclusion. She’s on a soft / wet foods diet right now. I personally don’t like this vet but it’s one out of two options and the other vet gave previous (otherwise mostly fine) pets medicines that caused my babies to die a few hours/days later. So yeah... I don’t trust them.

Although this vet put one of my other babies down and they seemed to not care, I could not be with her at all and I had to say goodbye in just a few minutes with the vet standing right there before they took her away and then I received a taped up box a while later. Not a good experience!

But anyways, it’s for my baby girl and I was wondering if they can’t do it without sedating her, will that kill her? I’m sure it wouldn’t be an anesthetic completely but just like a drugged/hazy sort of thing.

Would it be like a gas mask and is that safe for my rattie girl? Her being older (almost three years old, to my knowledge!) and I don’t know what’s going on inside of her.
She does have a weird tumor on her stomach that like splits into two different tumors and it’s soft, it’s weird. I’ll have the vet look at that as well. But I’m just freaking out right now wondering If tonight is my baby girl’s last night.