"Sound reasoning."

Yes, she would be more capable of heaving the other young woman down, if this somehow goes terribly wrong.

"I'm an Alethi woman, we don't credit luck. But I wish you focus, and I'll be right behind you."

Literally, because she's coming part way up with her, so she can grab on in a hurry if she has to. She could probably get Hermione down the ladder without breaking both their necks.