How to handle a person wanting attention on them during a family death

I’m pretty good at nodding and smiling so I ended up with the role of dealing with my best friend’s mom during the death of my best friend’s child.

They have not been seeing I’d eye for a while and my best friend doesn’t want to deal with her mom for the last few years wanting her attention. But now her child died and I think her mom, maybe with some dementia, is getting nutty. She’s making the child’s death about her. Let’s call my best friend Sarah and let’s call her mom Susan.
Sarah’s child is on her death bed waiting to donate organs and Susan showed up from out of town since the grandchild is dying. It becomes night time and she apparently yelled and demanded that since she can’t drive at night that the father needed to take her to the hotel. The father said he’s not leaving his dying child’s death bed and she can find her own way to the hotel. I agree with him.
Apparently in the waiting room Susan said ” I guess nobody cares that I’m the grandma too and Ill just sit here sucking hind tit.” Even showed up in her “grandma” sweatshirt. I think everyone rolled their eyes at her and left the room, I wasn’t there. I can’t believe she said it out loud so I’m thinking the dementia is getting her. Susan had previously run back home out of town and returned and since then the other grandmother has started organizing a memorial. At some point all of this Susan had called me complaining no one is giving her details and she’s not on Facebook and I basically did the nod and smile and that I will take care of you, hang with me, because I know everyone is hurting. This grandmother was the one who raised the child from infancy to school age while parents were at work so I do feel bad that the child was kind of her baby too. I informed Sarah her mom had called me to complain so I gave her to the attention she wanted; I told Sarah I would run some interference.

I’m going to need some advice on how to handle Susan because apparently now she’s spouting ridiculous shit like what about her, she’s over here “sucking hind tit.”

Bro it’s about the dying child not her.

Advice on how to tactfully tell her this and get her to stop demanding to be catered to because she needs to chill. We have two memorials to get through and I’m pretty sure I’ve talked to her into not going to the third out of town that’s kind of for the child’s school family.