I completely changed career at the age of 50 and it was a ray of sunshine, dragged me out of a rut at a time when the family were fleeing the nest and generally gingered me up.
Is this something that you could research? I was a social worker but changed into a freelance photographer, picture editor, singing workshop leader, arts outreach coordinator, community choirs leader. Could not have been more different!
Do you have any interests from long past, or talents that went unused? Or something that you always fancied trying but never got around to?
Could you find the courage to think out of the box and look forward.
We all have regrets about the past and concerns about how we parented and the mistakes we might or might not have made, but the future is the way to go. Looking back does not help.
If financially you might be able to have a "while not working" then plan how you might use that time to forward future plans - e.g. do a course in something that might have earning potential - I did a part time photography course and it opened up lots of doors for me.
Above all you need to try and find a way to think positively about yourself and sell yourself as someone to be valued. Try writing down all the things you have achieved rather than dwelling on those things that did not go perfectly. You brought up a daughter on your own - that is an achievement - She’s now very successful and has an amazing job and it’s lovely when we meet up! - sounds perfect to me!
My DDs learned a lot from how I made the career jump - notably that you can do new things and make fundamental changes and need not be stuck in a rut.
I hope you will find a way to move forward at this new stage in your life - the world is your oyster!