Please don't base your decision on our opinions. You'll find there is really no gray area on this subject in the responses you get. Many moms believe preschool is completely unnecessary. I happen to disagree.
My kids are in full-time day care. We spend a lot of time with them on our own working on letters, colors, etc (they're 2 and 4), but there's something about learning from another authority figure, outside of a family member, that is really helpful to kids that age. It's not to say you're not capable, but your message already recognizes that she's not truly comfortable in situations where you're not with her. That would be my first sign that I needed to get her acclimated quickly.
All preschools are different. Don't assume she'll get bored because she's picking-up on things quickly now. Our day care has a set curriculum, and it's as much an educational as social curriculum. Last week, they learned all about baseball. This week, it's geography. They assign jobs to the kids such as "Botanist", "Zookeeper", etc.
The conflict resolution, dealing with different personalities, following directions are things that are difficult for us to teach as parents when we can't immerse our kids in that environment without being present.
I've seen a lot of posts insinuating that I'm not as good of a parent because my kids are in day care and don't have me there to teach these things full time. In our case, this is the best decision, and I don't have regrets. I hope you're able to find make a decision that works for your family as well and don't have regrets.
Good luck.