Do I have to go? (Funeral) (update in OP)

Update: I told my mother I am not going. Instead? we got my mother a plane ticket and hotel room for the funeral. One of the main issues was that the other sister who is flying in, who is financially comfortable and/but very cheap, was insisting on sharing a hotel room; given the fact that my mother has been ranting nonstop about that sister for days, I am pleased to say I persuaded my mother to get her own room instead. The other surviving sister is going to drive in for the funeral. I am extremely relieved not to be going; until the date turned out to pose a problem for me, I don't think I realized how much stress I felt about probably having to deal with yet another blowup/meltdown.

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My aunt died this past weekend.  I have not seen her in fifteen years, and we were not close.  She was one of my mother's sisters; they were not particularly close, but they were sisters (my mother hasn't seen her since the last time I saw her; they talk about once a year on the phone).  My mother is very upset about losing her sister, and I am sure that it has been made 10,000 worse by the fact that my father died under similar circumstances (in hospice) a few months ago, and because my uncle asked her not to fly down during the couple of days between her entrance into hospice and her death.

I had originally planned to go to the funeral, to support my mother, even though I would not otherwise go.  However, for various reasons, they've now scheduled the funeral for a month out, right in the middle of my family vacation (it would not be possible to do both).  In addition, every time I tried to talk to my mother about making arrangements prior to having the date, she started screaming about how terribly my uncle had behaved and how awful her sisters are and so forth.  I would say, hey, she is grieving, but, also, one of the reasons I am not close to her sisters is because, over the years, at pretty much every large family event, my mother gets into a screaming fight with one of her sisters in front of the gathering and storms out, and then doesn't speak to them for years.  She's clearly spoiling for a big fight here.

So I don't want to go.  I don't want to cancel my vacation and it can't be moved.  I don't want to pay for a plane ticket and deal with this drama.  I'm in therapy right now to deal with my father's loss and the idea of going to a funeral for someone with whom I wasn't close sounds terrible, particularly if it's going to be like the other family funerals my mother has gone to where she has made a scene.  I sent a Harry and David basket to her one kid who I could find and wrote a nice card.  Can I just let my mother go on her own and sit this out?