I guess they were never really close but after Sienna started having those dreams about the future she realised that her mom has been manipulating her for years behind her back and that made her very suspicious about her mom.
On the other side, her mom realised that the control she had over her daughter is being lessened and that Sienna is making more autonomous decisions and she's trying to gain that back before Sienna becomes more powerful.
They don't have a bad relationship. The fl always thought her mum was the only one she can trust. But when she started seeing the future she realized otherwise. And found out her mum is constantly keeping tabs on her and making her teachers lie to her about her excelling in the subjects she is being taught.
Wait why does her and her mom have a bad relationship? I totally forgot the details