Her body language towards Twi'lek slave girl made me think that was more her idea than Boba's, like Boba was indifferent towards her, he only cared about killing the potential threats, and it was Fennec who was giving her the "Go ahead, get out of here" head nod.Absolutely!
A point I forgot to make was that, as far a Fennec goes-
Yes, she's the one that didn't shoot the slave girl, but she's also probably following Fett's orders, so that was more than likely his call, not hers.
I can totally see morally gray/ambiguous character such as Fennec having a soft spot for children/other women, but being more than willing to shoot a local constable or a random civilian driver. We don't know Fennec's full story, she might have been an orphan/street rat herself, or been forced into some kind of indentured servitude, and those types might strike a nerve with her. We've seen plenty of other Anti-Heroes or ambiguous characters in the past across all types of media who have had the "No Women, No Kids" moral code. So, Fennec might be willing to kidnap Omega, or another kid, especially if Fennec is being hired by the Kaminoians to "Bring Her Home," but she won't kill them or go out of her way to hurt them, and it doesn't have to be a plot hole or a characterization. People are complex, messy things, and maybe that's what we're seeing here.