Gemmy was patient as Murdoch got ready, not standing up until his pack was on his shoulder. "All right then, Doc. We're headed toward the gates."
She did not, in fact, take the lead. Rather, she walked to Murdoch's left, and ever so slightly behind him. To a casual observer, it wouldn't look out of the ordinary at all, but Murdoch would probably know what she was doing -- with her behind him, and on his weak side, any attempt to cause a stir would end with his quick yet painful death. Especially given that anyone running errands for Tall Johnny, even on an ad hoc basis, almost certainly had an extremely high degree of skill with a blade.
When she wasn't busy talking someone's ear off, Gemmy had a knack of blending in with a crowd. No one would find anything remarkable about the thin girl shuffling along the street, and indeed, no one gave her so much as a second glance.
The Knights at the gates seemed completely unsuspicious of her as well. What was apparent, at least to someone who knew what was going on, was that, if one didn't want to attract attention, Gemmy was a good person for the job.