Your temperatures actually don't sound bad, but you should probably raise them if she's getting sick. I believe they're cause by low temps and low humidity.

I could definitely be wrong but the only thing people seem to mention in conjunction with mucus is respiratory infections, and it's always what they say to look for if you suspect one. It's a big sign. They don't just go away, even if the symptoms do. She will need antibiotics.

Is the enclosure kept clean? Is the substrate dusty? These might also cause it.