If you do not think she will be completely in control of her toileting.... and fully "trained"... I would ask the school- "What then?"
Or, some schools do accept diapers. Some do not.
Or, you just put her into school when she is toilet ready.
Since you are a SAHM.... then perhaps you can hold off, until she is ready.
The more pressure she gets about it... well, it won't help.
Most kids.
Myself, I can't potty on command either. LOL
Going poop, is often the 'last' habit to be completed. And "night time" control is an ENTIRELY different time-line.
FOr example: I started & introduced "toilet training" my daughter when she was about 2-2.5 years old... but slowly. I gradually built up to it over time, and my "expectations." BUT, it took about a year... to where SHE was consistent and open to the whole idea. BUT, with pooping, that was the 'last' one to complete. AND, then "night-time" control sans "accidents" was when she was about 5 years old... which is normal and common. Some kids are even later when they attain night-time control, sans accidents. On their own.
My son on the other hand who is 2.5 years old, is just not ready yet. So I am not doing the toilet training yet with him. I am still thinking about it. He is just different than my daughter was.
Ask the school first. See what they say. Or, if you must enter her into school already, then choose a school that does accept diapers. Or just hold off, if this is the school you really want. Have you paid tuition yet?
each child is different is how "quickly" they will competently complete toilet training. But, regressions are common too. So expect that. Nothing is wrong with that. They are still so young to be "perfect" about it all.
Don't feel bad... toileting can take lots of time. If they are not ready. And "accidents" will still happen.
Is she going to pee at-will, on her own? Or only when you take her every few minutes? Can she wipe herself? Does she wear panties or pull-ups? Does she ASK to go potty... on her own? Or only when you take her? Can she pull down her pants/panties herself and hop on the toilet herself? Does she KNOW to ALWAYS wipe herself from "front to back" only? (which is important for girls due to infections), Is she dry for a few hours on her own?
If not, she is not fully 'ready'...
And no, 'rewards' and candy will not always work, to make them toilet trained. It never worked with my daughter.
As Julia M. said, if the child is not ready, there is nothing you can do, to "make" them or speed it up. Its a process. But when they ARE ready, it does not take long.
All the best,
Susan