Curious on her age... certainly that would play into it.
If she's approaching her 30s or 50s there are some hormonal changes to be expected - getting blood work would help for sure. If she's on the pill (or recently come on/come off) that can play havoc with libido too.
It also makes sense to look at her diet/sleep schedule too - not enough fats = hormonal issues almost certainly.
As for as the chemistry department goes, you could look into PT-141 (an injectible peptide) or poppers (amyl nitrate, inhaled). Not sure if any of those would be worth investigating.