She is very acrobatic and slippery. In the period between when she left home at 15 and when she was recruited, she was probably stealing to survive and he might have caught her but saw the potential in her Disney's Aladdin level antics? Like, hey use your crazy climbing skills for good and to help us disarm dungeon traps and you'll be able to afford your weight in hedgehog pie. Or whatever sales pitch would be in character for him, lmao.