Hi and welcome to this chat room.

I would for sure take her to the vet. She may just have a little bug but you just can't play with that stuff, especially with a pup, their ammune systems are not nearly as developed as a grown dog. It could be something minor, but what if it's something that is advancing with every day she is not on meds or treatment.

By the way, Lexi is an adorable name Good luck with her, hopefully it's nothing serious.