I think, only now that I am a mum myself, I can give other mothers the grace they truly deserve.
This is only my personal experience but I know my daughter will not know me to be the carefree person I was pre-DC. I feel like as mum there is so much more responsibility than I ever had before having DC, I am winging it whilst also being in therapy for anxiety and praying I am giving her a happy childhood and I don't mess up. I think some people are amazing at being parents, and are very good listeners and patient and all the other good qualities but for some it is that little bit harder.
My own mum, on threads I've made about her, could be described as toxic. I feel like she is so persnickety with me. But I also knew how young she married, the unbelievable stress she was under, how she couldn't bond with her babies like she wanted to, and she is an anxious personality. And I also know, because I'm the eldest child, whatever I go through, she is going through it for the first time as a parent even if she is in her 50s... I know she sacrificed so much for us to have a happy childhood, she gave us healthy meals every single day, was always there on time for drop offs and pick ups, we were clean, well dressed children. With my own DC, I marvel at how my own mum managed it all (things I previously thought were simple everyday tasks, some times just feel exhausting and neverending for me).
This is a very long way of saying, it is sad that she couldn't be the mum you needed, but also, maybe she was doing her very best and at least she managed to show up for you in other ways.
I am in awe of mothers since becoming one myself (it really took having my own baby to really understand motherhood).