Vet help please. Enlarging lump.

I have a 20 month old CLF that has a swollen lump that is slowly enlarging. It is roughly 3 inches by 5 (fits in my hand) and on her right side beginning at the end of her rib cage and going to her hip. I will be getting her taken to the vet tomorrow! I am only posting this for any reasonable advice that may help her tonight. Here is what I know. Notice the lump yesterday when she was outside in the sun. I did a circumference measurement on it and she was 21.5 yesterday and almost 22 tonight. Her temp is 103.4. She has slowed down a bit being a controlled but fast athletic dog neaning mildly lethargic but not much.....more like she doesnt feel quite right. Still no lack of enthusiasm. She went after a mark the 7 year old threw before I got her called inside. She is very lean so the lump is very noticeable. I will try to attach a couple pics. I have access to a thermal imaging camera through work also. It shows a definite temp range and irritation. She has no loss of appetite, still solid stools, no problem drinking water etc. Even picks her head up when I walk across the room. I am thinking a spider bite. Any ideas or suggestions??? Other than that she appears to be ok. The lump is also very hard and tender to her if I put pressure on it she will pull away or start to lightly whine. Bottom pic is a normal standing pic her on point with a quail she found in the garage. I also felt through her fur for a sign of pucture from a seed or thorn as well as a bite sensitive area. Nothing really has turned up or evident.