The Plague Mother decided to build her base to a hex where I had previously built a resource collector. Which is quite odd, because I didn't lost my resource collector, and she never moved again to another hex from that point. I was able to see her activity (which was doing nothing) because I still maintained vision from my RC, which appeared to be inside her base as a second facility.
Vic, if you would like to see for yourself, I have the save file available.