I committed a cardinal parenting sin. And I feel so guilty.

I totally missed something super important to my 6 yo - her kindergarten graduation. Now, she goes to a different school than my older 3 did, and they didn't have any such thing as kindergarten graduation at their schools. I remember reading about it a month back or so on the school calendar (all it said was 'kindergrad' and no info on what time or where) and wondering what it was exactly. I figured her teacher would send me an email before it happened. I should've known better - they had the graduation a few days ago and I didn't go. My daughter came home upset that she was the only child without parents there. I felt sick that I missed something that important, and angry that her teacher didn't contact me or email me.

One thing I've noticed where I currently live is there are tons of stay at home parents, mostly moms, and that the dads all own their own businesses and take time off all the time to go to school functions. I'm a single mom of 4, and I'm in school full time. I recently had to write a national exam (to try to become an accountant) and so I've been somewhat absorbed in that. I have only had the time to go to the school and talk to the teacher once in the last month. Apparently, all the other parents talk to her all the time, so she sees little need to email, which makes me angry. My older 3 all have teachers and schools that email constantly, especially before large important events. I guess I've come to rely on those emails too much - and I expect them. Over the last few years, every teacher has emailed regularly, until this year's kindergarten teacher. I talked with her on the phone the week I had my exam, and I remember telling her that I needed an email with important dates because I was very flakey lately with all that's on my mind (we just moved too, and I just got served with divorce papers - finally - and my oldest dd is going through some serious depression and I have some health issues going on....and my ex is not very involved with the kids on a day-to-day basis). She said she always sends emails. I told her I only get a few. I talked to other parents who said she doesn't email much.

So with everything going on, I feel super overwhelmed. I have family nearby but they are little help. My mom's idea of helping is to take the kids to the lake for the weekend - something I don't approve of because her idea of safety around the water is not ideal, IMO. Besides, I don't need to be relieved of my kids as I enjoy having them around - I need help with the little things like cooking or cleaning. Again, my mom's idea of helping was to hire me as her housekeeper. So I clean her house in addition to everything - but she pays me so I feel like I have to do it, even though it's super stressful. I get jealous of those families with 2 parents, with a stay at home mom - that used to be me. I never missed anything like this before, EVER with my older 3. I feel jealous and guilty and like a total failure as a parent.

Anyway, so I when missed the graduation I apologized to my daughter and told her mommy didn't know about it and that I was sorry she felt sad and alone, I reassured her I loved her very much and I really wanted to be there with her. I told her I would try to make it up to her and asked her if she could think of anything that I could do that would make her feel better. She listed off a bunch of things (play a board game, have a picnic, etc) that we've since done, but I need some reassurance from other parents that she won't be scarred for life. I'm very angry with the teacher but don't know if I SHOULD be (for background, I had a dysfunctional upbringing and am awful at knowing what is normal or what isn't. I'm also very conflict averse.) after all, it should've been up to me to find out what was meant by 'kindergrad'. Any ideas on what I should say to the teacher or if I should bother? Tomorrow is the last day of school, but it's just a picnic and then early dismissal so somewhat an optional day that my dd has decided she doesn't want to go to. I don't even know if it's worth it to bother to say something.
TIA for the advice.