Just show her the same civility that you would a distant acquaintance.

I have not seen mine in 3 1/2 years. She lives far away, which is fantastic. The only event I would ever see her at would be at a family funeral if DH wants me with him.  I will be polite but ignore her for the most part, but after the funeral go back to the hotel. I have no interest in hanging around that train wreck.

Treat her like you would a crappy coworker: polite, professional, and impersonal.

For peace you have to stay away from it, if dadddeee cannot correct the stupidity. If forced to be in the same place I would speak back about one word and leave the area she was in immediately; regardless of what dadeeeeee decides to do. I have no obligation to do anything for him around his brats, he never earned that respect.   I only do what I do for me, it is now all about me getting away if they are ever around me. I have not seen mine in years either and it was the best decision I ever made.  If I can never see them again, it will be way too soon.

Also have a plan with your DH that you check in with each other periodically. My DH would get so caught up in his kids that I became invisible. Very uncomfortable. 

After one particularly powerful meltdown where I was able to force him to look at his behavior, he has been super good about demonstrating care for me too. Makes these events so much easier.

That event happened probably 10 years ago, and DH apologized to me again about it maybe a month ago. He did not recognize his assholishness and was shocked to realize how badly he was acting toward me. 

I want him to have a loving relationship with his kids, but he’s still my husband. One doesn’t negate the other. 

This is a tricky situation.  I have stopped trying to converse with SD but do have to attend family events.  I hate it. I try to be civil (as was mentioned above) but she is not.  So I ignore her which then makes others feel uncomfortable.  It is frustrating and NEVER enjoyable.  I am toying with the notion of skipping all such events which would be a shame.

If I have to attend an event or have SD35 at our house (infrequent but annoying) I am polite but firm, I used to try and be as nice as pie and then had to listen to the constant nonsense she spouts. Now, if we are at an event I am polite but try to avoid her as much as possible but if it's in our home and I disagree with something she says, I let her know. It is my HOME not hers and I will not be subject to her crap anymore, as a consequence we rarely see her, fine by me. My DH catches up with at her place and I don't have to put up with her much. Not sure my DH is that happy with the arrangement but until he realises that the princess is not perfect then this is how it will be.

Good luck, it's not easy but I do find it getting easier with time.

I feel ya.  I'm new to this disengagement so to speak.  I have two SD's that are 18 & 21 now and could honestly careless if I ever set eyes on either of them again.  Absolutely no love loss.  So at this point my game plan is to treat them as a co-worker that you don't care to have a relationship with but need to remain professional (like Aniki suggested).  

At events you balance how you deal with her based on her behavioral choices.

You do exactly what you just said; be polite and talk with her if she addresses you, but otherwise don't fall over backwards trying to socialize with her

Treat her as you would a co-worker of your husband's, not someone you particularly like but still need to occassionaly be in the same room/function with, so you politely smile and wave, but then carry on with your life 

I have made the decision after 20 years of trying to block the SD31 from my life.  For more that 20 years I have tried to show her love and be there, but I am done being the punching bag.  She blames me for her Dad and Mom not getting back together when her Mom was screwing everything in the county and married her brother in law, but I digress, thankfully they live far away and I don't have to deal.  I told my husband that he an talk to them see them whatever but I will nto be around.  Also I am usually the one that does all the birthday and holiday shopping, so not sure how all this will go because I am not doing it anymore.  Should I leave my hosue when they visit?

Unless you decide to do something fabulous for yourself.  I was faced with this. On principle I did not want to leave my own home.  But by the same token, I couldn’t stand seeing them.  So I booked a spa treatment and loved it.  I came home pretty and relaxed.  So, consider this as an option.