@goldfish178 Because it’s suspicious that she knows the solution to heal her..In those times such plots as poisoning people and various other things to garner trust...say best example is someone being attack by bandits but those bandits are your friends or people hired by you so you can gain their affection and trust or gain something more Materialistically valuable...
Either way Granny thinks she poisoned her so she could get tips on how to advance by faking kindness
Gran-gran on the offensive! I think @Mewples is right about the poisoning thing, but once granny realizes Han Fei is legit, she's probably gonna become an incredible ally in that den of snakes.
@Kuroku2 : Yes...I too have heard: "Either you know it or you don't." "Either you did it or you didn't." (mostly related to homework, when you tell them you did some)