I told my parents about my married girlfriend over a year ago and at the time my mom was pretty displeased and upset for me... she kept saying stuff like "You can see how a parent would want their daughter to find the one person she can be happy with." She didn't ask about my girlfriend for almost a year. Now she's gotten much more calm about the idea... I can bring my gf and she'll ask questions and actively seek to understand the situation. She is even open to getting dinner with her at some point.
Basically, her seeing that I'm still happy a year later and that nothing catastrophic has happened has made a biiiig difference.