You need both the "Stabilizer" & "Hands-Free Mount" upgrades.
Get her on her stomach, shift both of her legs up so that she is in the doggy position, lift her shirt up (if you haven't removed it already), slide her panties to the side, then select the penis icon (4), and penetrate her.
If you aren't seeing some of the options, you might need to use the down arrow on the left hand side to adjust the view lower.