WIBU not to go to my daughter's school play?

[unreasonableuna]

Hi. I've changed my username for the purpose of this post. Obviously I can't decide if I'm being unreasonable or not, and would appreciate your thoughts.
Ex husband and I divorced some years ago, after he cheated on me. He is still with the other woman. He and I have little to do with each other, now that our children are older and have their own phones etc. His partner hasn't bonded with our children at all. She doesn't have kids of her own and made it clear she wasn't interested in anyone else's. So she never goes on holiday with my ex and the children, never goes out with them in general, not even for a meal. She takes no interest in their lives and in fact goes out of her way to avoid them when they stay every other weekend.
Whenever ex husband and I have had a joint thing to attend - such as a parents' evening at school - she has never come. I have never so much as clapped eyes on her.
My 13 year old daughter has a big part in a school play next week. Ex husband has decided to bring his partner along. That is fine, but I just don't want to be there. I know it sounds silly and vain, but I'm menopausal and have put SO much weight on. I look and feel dreadful.
It goes without saying that I never would want to miss my daughter's school play. So I decided on a genius compromise well I thought so anyway. She attends a small private school that is pretty relaxed. So I emailed the teacher to ask if it would be possible for me to go to the daytime production of the play, which is for the school staff and pupils (families go in the evenings). The teacher was more than happy for me to come in the afternoon.
Thing is though, my daughter isn't happy about it. She's saying it's embarrassing that I'm going to the non-family showing. I highly doubt anyone would notice my presence, but there we are. My work owes me some time off, and I was going to organise that. I was looking forward to watching my daughter's play in a more relaxed way. I'm not an anxious person, but the thought of attending the same one as my ex and his partner makes me feel awful.
Am I being very unreasonable? I'm just trying to please everyone and clearly failing
Thanks.

Just got this far and am glad you decided to go. Bravo. Good luck; but it will be fine and your daughter will appreciate it. :)

Thanks for the well-considered replies. As per, the vast majority are fine and I absolutely don't mind being told that I'm unreasonable, but a couple are absolutely nuts Emotional incest? Bonkers. I hadn't even told my daughter the reason I didn't want to attend. And as my update shows, I took the comments here on board and decided to go to the evening one anyway!
No need for me to reply further really, but thanks again to everyone else.

Hi- congratulations to your daughter on getting a leading role, how exciting! I suggest you do go in the evening. Get a front row seat and don't look back. Once. Nice dress/top, hair well done, and don't turn round. Have an exit strategy or a friend to sit with at the end. I'm sorry they're such a distraction on what should be a wonderful, proud evening.

Ah I understand why you feel this way and you are not being unreasonable about that. I'm glad you are going though. The only one who should feel awkward is that awful woman. It will mean so much to your dd.