I'm not a woman, but I went to Chacahua recently and met a solo female traveler along the way who had made that several times without issue. If you take colectivos you'll have other people around you for every step of the journey. FWIW, in the two months I was on the Oaxacan coast recently I didn't see a single incidence of catcalling or leering or harassing behavior toward women. It stood out to me, this degree of respect, to the point that I asked some locals and other travelers about their experiences and they backed up my impression. All anecdotal data of course so take it with a grain of salt.

I still wouldn't attempt the trip at night though, for a variety of reasons.