Wendy was definitely frustrated / angry because of how Aiden immortalized(?) her without asking her.
But Wendy never hated Aiden. (Even after he did this.) That's why she could forgive Aiden so quickly.
Also, Wendy's idea of oath of honesty was a pretty good revenge for him.
Because Aiden extended her life "a lot" without asking Wendy.
In return, Wendy will die if Aiden is not being honest with her, (he made that extremely unfair vow to prevent his nightmare, which means Wendy's death, from happening.)
if he lies again, that unfair vow will mean nothing because Wendy will die.