This is an interesting tidbit. So not only is she a complete slob, but you're subsidizing her lifestyle. I think you have even bigger problems than mold here. You need to have a "come to Jesus" meeting with this girl. Take plenty of pictures and tell her she has one week to get it cleaned up or you're taking the pix to the landlord. If she refuses or "just never got around to it" go to your landlord and lay it all on the line. Maybe you can't get through to her, but I bet the landlord can.
And stop bailing her out! You're enabling her to not pay her own way and then getting upset because she's not doing what she ought to do.

You're sending her a mixed message--"I'll be mad if you don't clean up and don't pay your way, but I'm not going to do anything about it. In fact, I'll even pay your bills for you!"
How much longer on your lease?