Girlfriend is friends with past hookup

My girlfriend has/had a friend and two years ago they were friends with benefits, giving oral and at one point in a threesome. They haven’t touched each other in two years but the friend clearly has had feelings for her. This friend also tends to talk shit about me to others. My girlfriend has claimed to not like her but still wants to hang out with the friend so she has someone to hang out with whenever but this makes me extremely uncomfortable, but she says I’m being controlling. Not sure what to do. Edit: She understands now. She said she doesn’t care enough about the friend.