Here are a few things that we did:
1. I kept a calendar that the nanny would use to document. (I wanted to know about his food intake and bowel movements--and I wanted it on record. But I also wanted to get right to nursing and re-connecting with him ALONE.)
2. She would call me on her way home if we needed to communicate further.
3. While I would get comfortable (undress, grab a snack, whatever I needed to help me settle in), she would take him for a walk or finish up an activity with him.
4. She would sit him down for a snack while she washed dishes or something, before my arrival. That way, he had already started detaching.
Maybe she's putting him in timeout because she is not prepared to handle him immediately upon her arrival. A timeout seems really harsh to me, unless he's kicking the walls. She's coming off dealing with whatever her day was and then traffic. Now, she's walking in to a screaming baby, not to mention how that can make a mama feel when her baby cries in her arms for someone else. Maybe you can let her get in and get comfortable--change clothes, use the bathroom, take off her make-up--not sure what kind of time you have. Mommy might need a period of transition, too. While you're updating her, let her be the one to tend to him. Let him see his mother taking over even before you leave.