No advice, I'm afraid. I just wanted to say that you're being very brave and are doing a good thing. I'm sorry your mother has taken this stance - it's easy to deny something like this, rather than painfully look at it head on. Victim blaming is also something people will try to use on you.

There's a line from Prince of Tides:
There are no secrets in my family; just denial.

I wish you the best in what you're doing. You are so strong.