I'm not really a big fan of female dom. I don't have an issue with changing things up now and then, but my limit would be at basic binding and light teasing. The more aggressive dom attitudes and actions (such as in the zip-tie scene) only succeed in eliciting feelings of annoyance or anger in me. That sort of stuff also shouldn't be done without prior discussion. Especially when restrained. That's more of an assault. Oh well, that's my opinion on that aspect, not that it really matters.
Anyway. I think it's pretty clear that the mother has multiple personality disorder or whatever it's called. There are just too many hints for it not to be the case (the last scene being the final piece in the puzzle). I don't have any experience with it, but it seems to have been portrayed rather well. The only question I have now is - how will it be dealt with? The MC realises that something isn't right, so I really hope he doesn't just selfishly go along with it without a care (which has the potential to lead to dire consequences) and instead actually cares about her wellbeing and tries to help.