You both need the time apart - I know it's not going to be popular among some of the moms on this site.
I didn't have an option. I had to go back to work with both kids. For baby #1 it was at 8 weeks. With baby #2, it was at 9 weeks.
Our neighbor's 5.5 year-old son started kindergarten a few weeks ago. He'd been in daycare, but it was a grandmother kind of situation, and the first week was a NIGHTMARE. He had serious separation anxiety and was not as well adjusted as other kids who had been in preschool, etc.
Just remember, the more time you spend together without baby sitters, other caregivers, the more she becomes reliant and dependent on you (which feels really good as a mom).
I like being with my kids. I've only been away from them on rare occasions when work required it. But, they've been in day care since they were infants, and I've felt very comfortable that they were in good hands.