I hadn’t considered the other response you got but it is very true! What I was referring to is your hand grip inside. Typically there is a bulb. If you are on top of her (prone) with two fingers inside, do a spiderman web shoot grip and see if you can feel it. Find it and grip it and work your arm like you want to rip it out of her. Definitely start gentle at first but IME the rough stuff will be well tolerated and enjoyable. Oh yea, set a towel down under her and probably a hand towel at the ready 😉
But be careful, being open source does not inherently make it trustworthy. It could be doing something nefarious that just hasn’t been caught yet.