Girls, Why does my girlfriend have to tell her mom EVERYTHING?

Short and sweet - my girlfriend tells her mom absolutely everything, and I'm not sure why... I don't mean just little things, it's absolutely everything. Crazy intimate and private things she will just spill out to her. I don't want to end the relationship, but this is seriously bothering me. I've asked her to keep some things private and told her that it bothers me, but it gets me nowhere. The last thing was something extremely private that I hadn't told anybody - she promised me she wouldn't tell anybody, then I find out the same day that she told her mom. I want to know why she feels like she has to tell her every secret we have, is that normal? Why would she not respect my wishes about keeping it private? Is there a better way I can talk to her about it? I don't want this to ruin us, but I'm not okay with her mother knowing every detail about our relationship, it makes me very uncomfortable around them.
Girls, Why does my girlfriend have to tell her mom EVERYTHING?
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