Talented mare Girl Guide has been described by her trainer as a stakes winner in waiting after backing up her younger sibling's impressive season return with a dominant victory of her own.

Girl Guide, an older three-quarter sister to Group winner Gregers, stepped out as the $2.70 favourite in Saturday's Dr Sheahan Plate (1200m) at Moonee Valley and raced to a convincing three-length victory over Jacinta ($6) with Esprit Rossa ($26) 1-1/2 lengths away third.

Her win came a week after Gregers resumed with a 3-1/4-length victory at Caulfield, and trainer David Hayes doesn't believe there is much between the pair.

"She has been working with Gregers and when Gregers won like she did last week, we were pretty confident this week," Hayes said.

"I think she's a stakes-winning mare waiting to happen."

Girl Guide is a five-year-old but only made her debut in February this year after breaking her wither as a young horse.

The victory of Girl Guide, the mare's fifth in seven starts, brought up a winning double for Hayes after three-year-old filly Afleet Esprit finished strongly to take out the opening event.

Hayes said the Group Three How Now Stakes at Caulfield on September 20 would be Girl Guide's next start to try to win a black-type race.

Trainer Mick Price has earmarked that race as the spring return for dual Group One winner Samaready.