The following information comes from the HomeSchool Association of California:
"We have asked the CDE if they agree that new schools can be formed after October 15, and, if so, when these schools should file their affidavits. The CDE told us that they believe that new private schools are allowed to be formed after October 15. They said, however, that these new schools should not file an affidavit for that school year, but should just wait until the following fall to file.
We agree that, strictly speaking, this is correct. However, because the CDE isn't the only government agency that has a reason to think about whether a particular private school is "legal," we are a little worried that some other government official might interpret the requirements of Section 33190 differently. For example, an attendance officer might come to someone's door inquiring whether a particular child is attending a legal school and not truant. That official has the right to see certain papers (see discussion at Section C of Special Situations). One of those papers is the filed affidavit. If the school was formed after October 15 of a school year and hadn't filed an affidavit, it could certainly explain to the officer how the CDE interprets a new school's obligations. But that officer might look at Section 33190 and Section 48224 and conclude that the school isn't legal because it hasn't filed an affidavit. We doubt that a supervisor or a court would agree with the officer's conclusion, but any parents wanting to shut down the possibility of ever having this argument might want to think about filing an affidavit anyway.
The CDE has said, in various years, that it won't "accept" filings after January 1. In early 2005, they disabled the online filing option after that date, but put it back up when a number of people and groups complained. We think they came to understand that people can file affidavits at any time, even if it is outside the October window. We believe that the CDE does not have the authority to "accept" affidavits (although they sometimes reject them for incompleteness), and so we think that schools are still entitled to send them. If you are trying to file after October 15 and find that the online filing system isn't working, you can still file a paper affidavit.
The fact that the affidavits are filed after the school year typically starts is not a problem. No private school can file before October 1, and the state does not claim that every private school student is truant between mid-August and October 1. If you are contacted after the typical school year begins but before October by anyone who has a right to see your school's affidavit, you should explain that no private school can file an affidavit before October 1. You can also offer to show them your affidavit from the prior year, or, if you did not file in the prior year, offer to mail them a copy when you can."
Here is the link for the page:
Please read all of it; I only copied part of it.
And here is another link entitled "Withdrawing your Child from Public or Private School Mid-Year". It will answer your question about what to tell the school if you decide to pull her out now: