There is a wonderful little common magic item that might fit the more adult theme of this game. Cast-off armor. It only takes an action to Doff(remove the armor) So all your sister would have to do is pull a pin and the whole binding comes undone and she stands there in her nude form.<br/><br/>The Illuminators tattoo is also interesting, able to write without pen and ink and can make up to a page of writing invisible to everyone but you and a named creature for 24 hours. Perfect for body writing kink if you wanna explore that. (I would deem you can wash it off. final say lies with Redknight though) It does take an attunement slot, but the wonderful thing about the tattoo magic items is they all count as one attunement if you have multiple tattoos.<br/><br/>In that Same vein, You can get The Masquerade tattoo.  That one is a tattoo you can cause to shift, enlarge and generally make it look like anything you want (can currently be the symbol of shar over her nipple) and once per day you can use disguise self (dc13)<br/><br/>I'm also sure that Redknight might not mind a little, Ahem, lewder adaptation of the prosthetic limb in the form of a magical strapon she can apply. once there it functions as the intended body part would, including sense of touch. (redknights approval on this one)<br/><br/>And finally, The Rope of mending could be pretty useful for you. Can cut sections off and stick it back together...I'm sure we can see some creative uses for that as well (shibari rope harness without any knots you say?)<br/><br/>Oh, one more. Shiftweave cloth can store up to five looks for clothing for you, speak a command word to change to a different outfit.