No school till 5

My understanding is that you can’t be fined for taking them out of school until they’re 5. Happy to be corrected though.

Legally You cannot be fined until the term after they turn 5, so yes in your daughter’s case it would be January.
However when you enrol them in school you are agreeing to an obligation to make sure they attend. So no you can’t really just have her off for random days here and there for an entire term.
She will still be expecting to attend fully.

As a teaching assistant, I’ve watched this happen, they learn a lot in that first year and she’ll only fall behind.

Yes this is true she wont be compulsory school age until the January. You might still get the attendance letter mentioning fines but they wont be put in place until she reaches that CSA. Sometimes parents email the head teacher saying child will only do mornings or they wont be coming in on fridays etc but ultimately you can do want with her days off/holidays.