Talk to it right off the back (Doc, "Hush!") and you can do this three times until "I got something for you" Edna dialogue option pops up. Think you only need the "hush" once though.
Choose "I got something for you" in Edna's dialogue tree, then talk to it before showing Edna Doc ("Nice Cactus").
Once introducing Doc plays out, Talk to it ("Help me out Danny"), then use the Flower on Edna.
Once that plays out, Talk to it while Edna is in the car ("Move faster Danny")
Trip the wire, now she thinks it's Strickland, but not. Talk to it ("Looks like a Strickland to me"). Put on wig, talk, put on hat for a cut scene. (might have to only get this response once).
Once that plays out Talk to it ("Got a point marshal") Then hang up saloon sign.
Talk to it for the last time ("Hey, it's your granddaughter...") and trophy pops. Now go play with fire.