Co-Op is more socialization not "academic." Some are less structured... and they 'allow' for kids still learning.
Pre-K... it is more structured, academic, and kids expected to know stuff. Also play learning as well. Since they are young.
In Co-Ops, parents help. In Pre-K, it is not a parental 'volunteer' geared thing. It is 'school.'
Ages in class, are more specific. Not all grouped together.
Your daughter will probably be fine in Pre-K.... that is Preschool.
It would be a 'transition' for Kinder.
AND per the influx of 3 year olds in her current Co-Op.... in Spring.
The thing is, IF you see/think that your daughter is ready for branching out.... then its great to move her to Pre-K. If not, then keep her in the Co-Op.
Girls, are usually more 'mature' than boys. My daughter was. She LOVED Preschool or Pre-K as they called it.
Regardless, the activities are age related and the learning....
At my daughter's school, they have a Co-Op as well. It is more 'play school' versus "Pre-School." Not as 'academic' geared, but rather, serves to teach socialization and 'routine' and listening to direction, and group activities.... for the child to learn in that kind of environment. I know parents who have had kids in this Co-Op, and parents who's kids were in Pre-K. There is a big difference. Pre-K being for structured and they are taught more 'academics' etc., and the complexity of activities, are branched out.
Me, my Daughter went to Preschool, from about almost 4 years old... and attended Kinder from when she was turning 5 years old. She was totally mature and ready and WANTED to go to school, she would tell us repeatedly, she wanted to go. She adjusted fine.
My son, on the other hand, who is now 4... I home-school him. He is just different from my Daughter, we can't afford Pre-school... and I feel he just benefits from being home, still, for now. Then he will either go to Kinder at turning 5 or when turning 6.... or attend the school's Jr.K program when he is turning 5. His birthday... is at the cusp, of the age cut-offs. So he can to either way, to Jr.K or Kinder.
Ultimately, just go according to your child, and their readiness, and if your child is ready for branching out, and being in HER age related group... then that is positive. If not, continue in the Co-Op. You can always teach her things at home too....
Either way, if a kid went to a Co-Op or a Pre-K program or Home-schooled.... they all will go to Kindergarten at some point. And how they transition/adapt... depends on the child. It is not a matter of one way being better than the other... because each child, had different dispositions... and rates of transitioning...
But, the basics of 'knowing' their ABC's, counting, numbers, colors, shapes, writing their name, etc., is an expected knowledge, that the child needs to know, per Kindergarten. Which to me, is not an age specific thing.