Now I know my son should have said no and walked away but for some reason he didn't. He cant explain why.
I have one of those. She had a phase of playing with a not-so-good kid and he'd get her to do all sorts of stupid stuff and she'd say "D made me do it" when I queried why the hell she'd do that. Fortunately she has no opportunity to play with him now but she still occasionally just does something someone else tells her to do, and can't explain why. She's odd, sometimes she can be very bossy and things have to go her way Or Else and she'll argue until she's blue in the face about something but at other times she'll just passively do what someone else (never me) says.

She has, however, got a LOT better lately in a lot of areas. She's almost 10 now and she was like yours at 7, so there's hope