My MIL is the same, defends her kids AND her daughters children to the end. No matter WHAT they do.
I hate to admit this, but I avoid her like the plague!
AND when I am there, if she brings any subject up that I don't take a liking to, I say something like "Whoops, I forgot, I have to go to the bank" or some such baloney.
There is NO changing these MIL's so, avoid, avoid avoid, and detach slowly, and surely.
Actually I think my MIL got the message cause she doesn't phone me anymore.
(unless she wants to use me for medical info, and I tell her she needs to call her Doctor)
Hugs and hugs......