Oddly Shaded wrote:
This isn't my pic because I don't have one on hand, but that's what is looks like kinda, but Slide's is a little bit bigger (and less noticeable because she's white where the lump is.)
I will look at taking her to the vet, but I just don't want them to suggest anything rash.
Hi Oddly! As above people said, the best is to take her to the vet

But I have three questions, first how old is she? is she neutered? How fast does the lump grows?
I ask because I've read mammary tissue in rats extend to their armpit and shoulder too... My rat Pepper at 2 and a half years old developed one in his armpit too. I could (thanks God) afford have it surgically removed. Tests reveled mammary tissue on the lump, so even for a male rat, it was mammary tumor, not cancerous though

The things to be more worried about are that the lump is cancerous and that it gets keeping big is more difficult to have it removed, it consumes the rat's body resources and makes difficult for the rat to move and live normally.
But this is my experience and what I read... Please do take her to the vet

good luck and say hi to Slide from Pepper and me
