My dog has a lump or growth between her toes. Will it need surgery?

Hi there! By the looks of the picture Olive may have a cyst in between her toes or even something like a foxtail or grass awn migrating around in there. There is also a small chance it could be a growth of some kind, like a tumor. It may or may not be infected. It's hard to tell by a picture.
Depending in what it is, it may or may or need surgery. Sometimes to get a closer look your veterinarian may want to give Olive some sedation and probe and explore the area. The sedation is recommended because it can be sore or painful, or even scary for her to try to do this awake.
Before jumping to any conclusions, I think it would be a good idea for Olive to have an evaluation by her veterinarian. They can see if she needs any medications or foot soaks, or even some medications for pain and discomfort and an infection. They can then determine if Olive needs some sedation to get a better look at the area. Foxtails can sometimes be fished out of their entry points using special forceps, and cysts can be drained or flushed if needed all under sedation.
I hope you find this answer helpful! Best of luck!