Wendy is only on the PC version.
Entrance: "Hey, how 'bout a kiss, Luigi-kins? No kiss? Then no brother!" (this is the one you were thinking of)
Click on her: "Still carrying a torch for me, hot shot?"
Complete a stage: "Big deal, one Portal locked. Return all the artifacts you want, Luigi-pie, WE'LL STEAL MORE!"
Complete leve: "Let's hug and make up, Luigi baby. Wendy wants violets, not smelly old fire flowers."