Level with her

Matt was in over his head, he needed information, and she was his best choice. She seemed impressed by him and he needed to know why she attacked him on sight.
"Let me stop you there. I just summoned this elemental today. I don't know why you attacked me or half of what I'm doing."
This time the elemental released her mouth without an overt signal.
"Well, isn't this embarrassing on my part. I'll make a deal with you. I'll make you my apprentice, making you a part of the initiated, and we never mention this again. Sound good?" she says, giving her tone a light playful tone that seemed out of place in the given context.
"Why did you attack me?" Matt asked.
"Well, as a rule we can't have anyone learning how to use spirits, they are powerful, but ultimately cause more harm than good unless the summoner is properly trained. So any uninitiated are taken care of. But you have a knack for it, I've nev-" the elemental again gagged her. It was responding to his commands subconsciously, that was cool.