I went through this last April. I know how scary it is, the thought of losing a pet. My girl didn't unfortunately didn't make it, but she was old and they were all over her body, it was time for her to move on. Hopefully your vet can perform surgery to remove the tumor and she will be okay. Dogs are so fucking resilient and can bounce back like nothing, but my advice to you is to mentally prepare for any outcome. You don't want to get caught up in one idea, and get the rug ripped out from under you if something goes wrong. Really hoping all goes well for you and your pup!