I too have Metacam for pain control. I've not heard of pills either but I remember years ago my vet didn't stock Metacam and it had to be gotten from a pharmacy. Perhaps that is the reason you got pills.
I'm glad you have pain meds. That will make her more comfortable. Be prepared though that the smell might get really bad, really fast.
Oral tumours are horrible. We have dealt with so many to the point that I was beginning to wonder if something I was feeding or doing was causing it. I charted everyone and found out that we had the average number of oral tumours per hedgehogs we had. When I removed the rescue/rehomes from the list, one that arrived with an oral tumour and a couple that developed one within a few months, then we are actually below the average.
You are lucky you have had her 4 weeks with her. That is a fairly slow growing tumour. I've had numerous that it appeared and the hedgehog had to be euthanized within a week. Our first experience was old Pagen. I discovered the tumour on Tuesday and we euthanized him on Friday. The tumour doubled in size daily. I swear I watching him that I could see it growing. He was still active, eating great, bright eyed and still enjoying life. The vet recommended to help him cross but my daughter and I wanted to give him a bit longer. She talked us out of it and I'm glad she did. She said that with the speed that tumour was growing, another day and his eye could be pushed out or it would reach his brain or the painful stage. Given that it was a Friday, there might not be a vet available to euthanize him on the weekend. At that time we had a rotating on call vet and we knew from experience that many would not look at a hedgehog. She also pointed out that we were there with him and could hold him as he passed and option we probably would not have with a vet that didn't know us.
I'll keep your little girl in my prayers.