There has been a lot of speculation on whether she's actually Ruka's mother or not for some time and it has been hinted a few times that Dr. Kurosu is in some way related to Ruka, but it seems pretty doubtful that she is her mother. Considering that Dr. Kurosu is a licensed doctor and apparently makes enough money to own a Lamborghini. While Ruka's mother was shown to quite poor along with her husband and lived in harsh conditions before dumping their debt on Ruka a little over eight months ago.

Wait for Hata-sama revealing is the best solution.