It could also work the other way around.
It's not so much a statement of her capabilities as it is a statement of her will. Her being unable to leave him there becomes fact because, as queen, she is declaring it so.
I see this as Starborn Molly influencing the mantle from within, esp the first instance. The Mantle is overriding Molly, but there Molly is making a Stark Choice not to be what already is as far as the Queen and Lady are.
These could still be considered bindings placed on who Molly becomes. So, if there is a Molly that is Mab in some parallel world, or that is ourMab, then she is now bound by Molly's will and statement. We do actually see each statement fulfilled by Mab.
1). Ramirez isn't alone as Mab stays with him.
2). Mab is still considering a better way and is open to it. Likely, she hasn't even yet found it.
Consistent with my Amberverse/Dresdenverse theory, there is a Mab/Molly parallel world out there that is feeding back through the Mab mantle. And, regardless of who "our Mab" is, she is attuned to these alternate Mab's and affected by them.