With respect to what MCaesar wrote, I'm very grateful for the criticism. It's definitely making me look more seriously at what I wrote/what I'm currently working on. I don't know what the etiquette is for responding, but I pretty much agree with everything you wrote. Touching on your points more specifically, though:
You're most welcome. I prefer "critique" to "criticism," though, as it's all meant to be constructive. Criticism has a bit more of a negative connotation. I hope it came across as "hey, cool story, and here's some stuff you might not have thought of." Gripe was probably not the best word for my to use, either. "Note" or "thought" would be closer.
Having mulled over the Mary bit, I think the story would benefit either from investing more in it, or as you said, paring it down. If you had made her a background character in Molly's story, then the focus would have been tighter on the scooby-gang, and you could have made the reveal of Mary being enslaved be a smaller, but still impactful moment.
I'm not a critic by trade, though, so take everything I say with a grain of well-meaning salt.