Babysitter refusing the go outside

My sons babysitter is part time and I depend on her to play with him and take him outside on nice days. I work from home so I've been leaving my desk to tell her to go outside and she tells me yeah they will go out but then doesn't do it. I'm not very bossy or confrontational and I don't want to lose her because she is very sweet and I trust her. But I'm getting pretty upset about her not going outside. It's 60 degrees today and sunny. She isn't opening up to me about why she won't go outside. How else can I bring it up to her? I offered her a sweater if she feels it's cold. I'm like the nicest boss to have and she is the nicest sitter so I don't want her to think I'm being a bitch by forcing her to do something she doesn't want to do especially if there is a serious reason why she doesn't want to take him outside and doesn't want to tell me.

Update: Until my son started crying (he rarely cries) she started to get him out. He gets bored in the living room watching TV. I don't understand why she waited until he started to cry and get bored.