Tessa expressed that although she doesn't like her grandma, she is still her grandma after all. Regardless, it's because of her that Tessa exists. That's the wonder of bloodline inheritance.
When it comes to familial love, sometimes it's not as simple as uttering a harsh word or deciding not to care; you can't just sever it cleanly.
Besides, if Faye were to drive her grandma crazy, it would still be her dad who suffers.
