Totally depends on the school.
At my niece & nephew's school in Tx, it was a requirement to ENTER K that the child be reading (a list of over 200 sight words was sent out), doing single digit addition and subtraction, and a whole host of other things. My nephew didn't pass the "test" so he was put in special ed (how the school got around no child left behind, was that any child who didn't meet the yearly requirements was sent to special ed. Which had over 100 kids in their school.) My nephew got "out" fairly quickly as he "caught up" to the other kids and entered K a year behind. My dyslexic niece was also sent to special ed... but she never learned how to read (until they moved out of district when she was 10) because special ed in her district in Tx was the "slush pile". Parents were considered responsible for getting their kids out of it by getting them up to testing standards. Special Ed was just glorified babysitting. So when she changed districts they had to start all over with 1st grade curriculum as a 10/11 year old... even though she's actually gifted... she had never been presented with curricula, much less given the mandated help for her disorder. She just sat in class and colored and played with blocks. Sooooo sad.
At my son's K... the school hoped (aka not even required) that by the END of K they knew most of their alphabet, most of their colors and shapes, and could count (out loud) to 20.
Same token, a person can homeschool and have their kids several years ahead or behind academically or socially depending on HOW they homeschool.
So will she be academically and socially prepared? Would it be hard to go two days a week one year and 5 longs days a week the next?
Totally depends on the school.