From what you have described, your daughter's lump is probably just a normal "gland." It has always been there, sounds like it doesn't bother her, it's not sore, and it's not changing or getting bigger. Parents also sometimes think about cancer when these lumps are first felt. In otherwise healthy, growing children, that is extremely rare, so blood tests and biopsies aren't routinely recommended.
I suggest not doing anything special. Watch for any significant changes in size or if it is associated with some local infection. Otherwise, simply ask your pediatrician to check it from time to time with her regular well checks for continued reassurance.