I don't know how to handle younger women.

I have a girlfriend and she's too young for me. We met during a new years party dating service two years ago. The problem here is that my millenial girlfriend and my daughter are having difficulties in getting along together. My daughter hates me for having a young girlfriend. She doesn't want to have a stepmother who is just few years older than her. My girlfriend on the other hand, always makes fuss about my daughter ignoring her. I already tried bringing them both to malls to do their thing, but it didn't work. It always ended up with my daughter leaving without telling me. I don't know what to do with them anymore. Any advice about this?