It does make sense, especially with Kyoko and Momo with the sister duo within the trio, and with the headcanon the shared element of one of the sisters being compromised by the job.
Although I'd change "The 1980's" to "20 Or So Years Ago", because unless it's really important for the events of the first game to take place in 2005 that would mean that Mikoto's mom would be in her 60s now.
Alternate Momo idea (not spoilering because nothing suggests this is true): She's an even more extreme version of what's going on with Takeru's organs, her body is entirely made out of demon bugs.
The original Momo was either captured or heroically sacrificed herself to save the other Black Cats and was devoured by demons, but her spiritual energy was so powerful that some version of her consciouness remained in the demons and now they believe they're Momo.