Because you are back at home with your mum, subconsciously, she reverts to your childhood, and brings things up from those times.
This behaviour is probably routed in her inability to accept that you are now an adult,the same as her, and that equality does not feel comfortable for her.
When she raises this history again, calmly and firmly talk to her.
Tell her that you are now an adult with your own views, and your own independence, and referring back to the past is pointless, and you want her to stop doing it.
From then on, every time she tried to take you back to your past, and she will, because it's a comfort for her to go back to times she understood more easily, gently but firmly remind her that you have discussed this, and you are not going to discuss your past with her any more.
Give it a couple of times, and if she still persists in bringing up your past, simply walk out of the room, each time she does it, and when you next speak to her, remind her again that it is not something you are going to talk about.
She will get the message, eventually, and it's time for her to accept that you are now a grown woman like she is, and you expect, and deserve, the same courtesy and respect that you show to her.
Good luck.