I have a bit of a dilemma and I'm not sure what my options are for responding without hurting anyone's feelings during a sensitive time. Here's what happened:

My aunt's mom (no blood relation - my aunt is my mother's brother's wife) has been in care facilities with dementia for years and passed away last week. I knew about it, but was not planning to attend the funeral, as I was not close to the woman who died and in recent years have not been that close to my aunt and uncle and their family (I have a large extended family). When her dad died a few years back I also did not attend that funeral.

The funeral is a 2 hour drive away next weekend. On Friday, my aunt messaged me on facebook to ask if I would play the piano at her funeral. I got the message this morning and didn't read the date right and thought it was today, so I responded that I was sick and couldn't do it....now I realize it's not till next weekend. The problem is, in either case I really don't want to do it.
Also, I am extremely out of practice! She claims it will all be simple hymns and things, but really, I am very, very out of practice. Like, I haven't practiced regularly in 10 years. My aunt is likely aware of this.

I think it's a little weird that she asked me, given that we are not that close, that I didn't know her mom that well, and especially that she asked me via facebook (she says she doesn't have my emails address but I am certain I have emailed her or been on emails that included her many times) and really just want to get out of it without offending her. She's pretty sensitive. I think she's a little batty with emotion at the moment and probably feeling nostalgic for a time when our family was more tight-knit. What can I do? What would you do?