From Muppet Wiki

Colleen Barker is the heroine of Dog City, as seen on The Jim Henson Hour. A collie and girlfriend of Ace Yu, her kidnapping spurs Ace into action.

On the later puppet/animated spinoff series, Colleen returned, with the same name, puppet, and performer, as neighbor and off-and-on girlfriend to Eliot Shag in the puppet framing sequences. She was abruptly dropped at the start of the second season, with the explanation that she'd moved out of the apartment building. Though the character was abandoned, Fran Brill continued on the series, playing Colleen's replacement, Terri Springer.