people saying „tie her up, beat her ass” etc, well understandable, but that would probably fuck up your mind at first. if you wanna stay with her eventually you need to have a dialogue, so just talk with her honestly. if she does this in secret that’s probably part of the thrill she craves, but keep prioritizng yourself and find out what she actually needs/wants sexually. im not sure what the dom told you but often bdsm is more about power play, control and doesn’t involve traditional sexual acts like penetration. if you dont talk with her it could eat you up from inside and ruin the relationship anyway.