Convince her you didn't intentionally get with a tranny and don't want one

You tell Stacy the truth. You shamefacedly admit that you did have an interest in transsexuals for a little while, but that the encounter she saw was **** on you. You even tell her that you went through with it to try and hide from her. Finally, you tell her you've gotten over that stage, especially after seeing that Stacy can fulfill your desires for penetration herself.

To your surprise and delight, Stacy believes you. She asks you to be more open about your sexual interests, wanting to know what about shemales is a turn-on for you.