Both of them are mentally ill.
Rena's got a job she hates and is doing what she can to keep herself entertained, but how do you see Sanae as being anything other than a nice lady who recently figured something out about her own sexuality?
It's funny, this kind of reminded me of ODD TAXI a bit, for the [potentially major ODD TAXI spoiler] way in which Rena occasionally lets slip that she sees the customers as fruits and vegetables and everybody else is bemused.Odokawa on ODD TAXI is probably the only person who sees the other characters as animals, based on how people react to his characterizations.
I also liked that Rena saw Sanae as a pear at first and then later comments on her shampoo having a faint pear scent, and the implication that she's perceptive, in her own oddball way. Again, like Odokawa in ODD TAXI, with his nearly preternatural skill to recognize people.