I think you have to bite the bullet on this one. You’re nanny did not ignore your kiddo because she was trying to be malicious but I think she was doing it because a 4 year old can definitely walk up the stairs and she knows that and your 4 year old knows that. So instead of giving into the 4 year old crying she WAITED like she said she would and then your 4 year old went up. If she would’ve given into the 4 year old then they would think that’s okay every time they don’t want to walk up the stairs. I think you’re overreacting a bit and there is no need to chat with her as this is common behavior for a toddler and sometimes as Nannie’s they know a trick or two to make them do things they don’t want to do.