She will most likely go to kinder in the fall after she turns five so you have a way to go.
You aren't "required" to put her in Pre-K, but even as a casual observer (parent) I was able to see a big difference in kinder between the students that went to Pre-K (or another "preschool" opportunity like Montessori) and those that were at home or in a "day care" setting before kinder.
My son started "school" at 18 months...I hired a nanny with early childhood education certification...she organized "school-like" activities for my son and her daughter while caring for him (nothing over the top...sorting games, manipulatives, etc...the kids loved playing school).
He went to a private "preschool" at 2 1/2 (as soon as he was potty trained)...still lots of play but they orchestrated plenty of learning opportunities (art projects, music, manipulatives, fine motor skills exercises). When I moved I found a similar school for him at 3 1/2 and he stayed there through kinder.
For me (a single working mom), it was well worth the expense to have access to all those people with training and education in early childhood development. They helped me identify any number of things I needed to do to help my son develop important skills (e.g., pointing out that he needed to spend more time coloring to develop finger muscles)...and my son was far more "stimulated" than he would have been in a pure "day care" setting. He loved it...and incidentally, he still loves going to school. In second grade, my parents had to drag me out of bed to get me to school...my son sets his own alarm and drags ME out of bed...in three years (kinder through second grade), I've NEVER had to "force" him to go to school...he cries when I make him stay home when he's sick!! I attribute some of his love of school to the fact that all the things he learned from being in a "pre-school" setting made the transition to formal learning a lot easier for him.