Could be shed but it looks like it pushing the lip apart. Maybe bug guts or something else she ate? Hard to tell, have you tried to manually wipe it off? Lol not sure if she would allow that.
If it doesn't wipe off try to get a look at the inside of the lip. I don't like how the lip is being pushed out. Any kind of discoloration is grounds for a vet visit.
The inside of the mouth should be one uniform color.
Could be shed but it looks like it pushing the lip apart. Maybe bug guts or something else she ate? Hard to tell, have you tried to manually wipe it off? Lol not sure if she would allow that.