Go to the Dr and get a check up...

Discharge in prepubescent girls isn’t common but it can have several benign causes. I’ve just done some reading and found the following helpful, it might be a little indepth though and I’m not sure if the link will work. I’d strongly suggest taking her to your GP to seek appropriate advice and treatment if necessary, especially if you’re concerned.
In the meantime try to eliminate any possible irritation from washing detergents, soaps etc in case it’s simply a sensitivity to something. https://obgyn.onlinelibrary.wiley.com/doi/full/10.1576/toag.9.3.159.27335