Both of my parents (uBPD mom) took me to my graduation rehearsal, an hour's drive away. They fought and yelled for the entire drive, with me miserably awkward in the back seat. Then we all pasted on our smiles and went into the rehearsal. Sadly, I feel like my whole memory of my high school graduation is colored by that part of it.
I truly hope your mom tones it down for your nephew's graduation and he has nothing but positive memories!

I think she's still trying to sabotage.
When I called and told her my plans.
1. She told me that it wasn't necessary for me to go. That he would understand. Besides her trying to sabotage, since she's refusing to go since she did not get to go to the pre-event.
2. Sister is having a HUGE party after the graduation. It's a joint event for several students since they have been together for the four years. She's hosting since she lives local -- only 4 or 5 miles from the stadium even. Other parents/families are helping with finances, etc. Mom is criticizing her for it. I intrepret it as jealousy as she has hosted prior parties for her grandsons at her house and she got to pick and choose who went and what was served, and all other control issues. She's not in this one.
3. Mom told me that nephew/grandson's other grandparents were going to be staying with her during the graduation because they are not "able" to attend. No, they are going. Even if they do not, they are not going to be at Mom's house. My sister told me that she's doing everything she can to keep them separate. Her in-laws live even closer that we do (and we only live a little over an hour away).
4. Mom also tries to control my Dad. He is friendly and can hit it off with anybody. She, being borderline, is not that outgoing. But she pretends to be very nice. She already told me that she is going to have to have a talk with him to keep him from talking too much. My husband and I agree that husband will try to keep Dad safe from Mom during the party. If Mom lets Dad attend.
5. I would not be surprised if Mom totally boycotts the party. She's not going to the graduation or the diploma ceremony. And if she does boycott it, everyone would be better off in the long run.
Sister is stressed by other things -- the event, her autistic son, regular life stuff. She doesn't need this. All I can do is listen to her vent. She called to 'warn' me and tell me that Mom's "on the warpath".