Watch for a little longer.

You decide to wait a little longer before you strike. The girls, blissfully unaware of your presence go about their business, making small-talk and gathering their spoils.
As the redhead continues to pay close attention to the outside, you can see the blue haired sneak up on her before suprising her with a swift smack to her rear. She lets out a yelp and begins scolding her fellow robber before she is silenced with a kiss as the blonde rolls her eyes, it wasn't hard to tell they were a couple. The black woman was speaking with the leader while she filled her bag, showing her a large diamond to which they gave high five to each-other, laughing.