Please take our advice with a grain of salt. We're all opinionated in our own ways for our own reasons.
I, personally, believe every child should go to preschool. My mom was a SAHM, and I was in preschool from 3 years until kindergarten. Part socialization, part recognition that I was a quick learner and to start preparing me more for full-time school.
I'm a working Mom. We're fortunate that our day care has a strict curriculum, and our son, at 4, could easily enter kindergarten this year based upon what he already knows. Much is learned at school. But, we proactively work to reinforce when we're with him, too. He turned 4 in June and blew away his developmental milestones at his well-child visit. We expect he'll be reading well before his next birthday - they work very diligently on letters, phonics, etc. in his class.
In-home day cares are more challenged from a curriculum stand point because they have such a wide variety of ages and learning abilities to incorporate. We'd looked at in-home, too, and we opted for a traditional facility because of the structure.
It doesn't mean mine is the right opinion - it's just how we feel in our house, and it's noticeable between our kids and others on the street who are similar ages who have not attended a more structured environment (speech, manners, socialization, etc).
Good luck. Perhaps involve her in the decision and see how she feels. If she's interested, I'd encourage it since so much of their fundamental learning is already taking place.