My Mouse is getting worse, please give me your opinions!

This is a hard one because sometimes it is hard to know how much or little pain your mouse is in, but it is very possible that the tumors are not painful, especially if she is active, eating, playing, running on her wheel and so forth. The signs don't seem to indicate that she is in pain, but of course a vet would be able to determine this better. If she was lethargic, listless and not interested in her activities or food, then that would be a solid sign that she is in pain. One of my gerbil boys, Mick, got a tumor, pretty big one, in his tummy area and it made him look pregnant actually, and when I took him to our local small animal vet, she examined him, did an ultrasound and after I told her he was happy, eating, playing, and doing all of his normal activities, she agreed after seeing the ultrasound and examining him, that although the tumor was big, he was not in pain. Due to Mick's age (he was getting pretty elderly) she said that a surgery would be a huge stress on him, due to his age and that since he was otherwise happy and content, to just let him be and enjoy his remaining time at home, rather than put him through the trauma, and possible complications with anesthesia. So that is what we did, and he had many more months of being happy and playing at home with his brother. (If he had ever shown the slightest sign of not being comfortable or suffering, of course we would have him put to sleep, just so you know. Animals should never ever suffer.) So, you might want to have her examined by your vet to get his/her opinion on this, but I think putting her to sleep when she seems to be a happy and active mouse would be premature. She sounds like a sweetheart by the way and I am sure you love her very much!

Thank you so much for responding Vladina, its very much appreciated. I'm very sorry to hear about Mick, he sounded like such a sweetheart.
The tumor he had sounds similar to what my lovely lady Kayleigh (mouse) had. I took her to the vet on December 21st, she originally went for a bump on her back which we discovered was just from her going into her house or playing under the other "furniture" in her cage, so i was given some antibiotics, that healed fine, while at the vet i noticed that her tummy looked very bloated, the vet thought she might have just been backed up and gave me a yogurt medicine for her. It helped her no longer be backed up, but the bloating never went away. She kept active until the day she passed away, Kayleigh and Piper loved eachother, Kayleigh's last day I moved her to the empty cage so Piper would not keep disturbing her while she was slowly shutting down, Kayleigh passed away on December 31st in the early morning. I sat by her side and let her know her mommy loved her.

For Piper we got a different treatment at the vet and a different doctor, i think I'm going to request her for my mice from now on, she seems to know more about them since she also is a mouse owner. She looked over Piper and ended up taking her into the back and taking a blood sample. At first she really though it was just an abscess, but then she looked at the cells and found it to be cancerous. The medicine she gave Piper did help her for a while, the original tumor stopped growing and her fur started to go back to normal. And now she has two more lumps. But still seems happy, as i said before. She still takes her medicine twice a day, I had to start rubbing it on her treats cause she hates it by itself (it smells horrible!). I know she will eventually have to go, but I want her to be happy for as long as i can provide happiness for her, cause shes my little baby. Once she starts acting as if she is unhappy or in pain, I will know it is time.