She's the FMC's mom if you didn't realise from all the hints they give us. She doesn't have people in her home, she wakes up, goes home, eats all by her self. Whenever she sees the actress she ends up feeling sad, and in pain. We see this first when she ran away from the actress when MC pointed out she was there. We also see this when she didn't want to watch the movie that the MC's sister suggested. So it's most likely her mom, and her dad probably divorced her mom and there was a big fight or something. There's most likely going to be a trope where the mom was just trying to earn money for her child but ends up accidentally hurting her instead (I've seen that a couple times.)