Slide your hand inside her shorts

Since Lin is responding positively so far, you decide to push things a bit further. You bring your hands back up to her back, then stroke back downward, sliding your hands inside her shorts.

Lin moans loudly in pleasure as you grasp her flesh through only thin panties, disengaging from the kiss and kissing down to nibble on your ear. You use your fingernails to scratch lightly up and down, and she shivers against you in response.

You pull your left hand back out of her shorts, rubbing her back inside her shirt, while your right hand teases and tickles as you stroke up and down the center of her ass. She's grinding more forcefully against you now, and her breathing is getting erratic.