I have 3 teen dc and live around 100 miles from my parents. Parents are in excellent health, retired for ten years and late sixities. We moved for context 12 years ago for work opportunities.
I had surgery two and a half weeks ago, a gall bladder and bile duct removal, which not the end of the world didn't come at the best time with dc all at home for the summer. It has been a struggle sleeping and quite tricky with dc all at home and no bus service here anymore. I am also have to WFH!!
We went to visit my parents last weekend, dd was telling her gps all about her A levels, how much is riding on them etc with her uni place and she was nervous. Gps wished her good luck, all good.
Fast forward to results day this week, and Dd is over the moon, she gets her grades and we are happy for her. She spends the few hours screaming and laughing down the phone to all of her friends, whilst I drop other dc to clubs and friends houses. I arrived home with balloons and a gift for dd and I drove to her friend's party and sleepover, picking other dc up on the way home and finally arrived home at 6.45pm knackered and sore.
I then realise my parents haven't sent a message, so I text them to say dd has done really well with exams and is overjoyed before trying to make dinner and sort out dc. My mother replies in a slightly hysterical way demanding to know why I haven't texted her before.
I said I haven't had the chance, I have been driving all day and can't text and thought she would know its all over the news and we only spoke about Sunday! I then get a series of abusive messages from her saying she is so angry, I should have contacted them immediately. It looks like they don't care about dd. How dare I not remind her, and I have broken her heart moving away and now 'ripped out her heart again' by not telling her about the exam results 
I replied calmly that I can not be expected to remind everyone of everything. I am permanently exhausted and its no big deal, dd is happy not the end of the world.
My mother is beyond furious and is no longer speaking to me.
Have I done something wrong here? She does not have dementia, she has nothing else going on in her life apart from seeing her local friends, I don't think she is being very fair - I have no idea why she didn't remember. I am only just managing as it is.