Welcome to the world of strange SIL's (could be all inlaws) avoidance tactics are great.
Rule 1. Never talk about mad SIL (unless drunk and your DH brings the subject up, that negates Rule 1).
Rule 2. She does NOT exist unless in an emergency. But the children do. And so does her DH (your DBIL). So don't omit her from conversation with them, but refer to her whilst thinking of her as an invisible friend, practice standard reactions to comments about her "smile, frown etc" NO rolling of the eyes.
Rule 3. Conduct all family business via DBIL/DH.
Rule 4. Retain moral high ground at all times, learn the art of pissing people of from afar, always send her an Easter card with perhaps a creme egg in it for her (in addition to the ungrateful children, it's not their fault) just so you can be smug and know that you've gone above and beyond duty (and in the knowledge it will piss her RIGHT off).
Rule 5. Never sweat it. You cannot change it.
Rule 6. NEVER EVER conduct any business with family on FB unless you're very very close and even THEN always be polite and ignore any shit unless you're fully prepared to accept the crazy consequences. For THAT alone, YABU there is a hide button for good reason. Your DH should have been the one calling her up on FB comments NOT YOU (unless you craved WW3).
My SIL is a complete Alien, I just don't get her on any level, and most of what she says is offensive. She is not on my FB. She would be hidden if she was. What I don't know I cannot comment on. If she was on FB and she has said something that discredited my DH, I would have perhaps posted some sage like wisdom on my own status, knowing she'd see it, or told my DH, then it's in his court.
NEVER EVER correct anyone on their own spelling/grammar on FB, on their own thread... EVER. Unless you really don't care about them, in which case why are they on your Friends List???? It's Okay to post LOTS of items about poor grammar, funnies about dogs refusing to even eat homework because the grammar is so bad etc., but never target anyone... again, unless you rather look forward to their wrath and make yourself look nit picky and rude. Again, hide if their typing offends you.
Families are crackers. I'm proud of the fact that my 'greater' family have no idea I loathe my SIL so much, they are aware she loathes me, but think her a fool. WIN!!! 
YABU to expect a thank you, but YANBU to expect that your DH receive one. Therefore, as no thank you happened, YANBU for being annoyed.