I don't know much about BDSM but this is very disturbing to me.
I agree with DH, get out and get your kids out of this bullshit now before any permanent damage, particularly to your children. She is obviously not thinking with a rational mind. After that, if she wants you all in her life, she will find her way back.
Who, in their right mind, would want to go to work every day with bruises/marks on their face?!?! Shit, I'm all for a little spanking, biting, little marks, where they can be HIDDEN, not on show for the world but visible markings, particularly on the face, neck area? BDSM aside, she needs some help.
Good luck to you.