I think you seem to have two issues, 'tired' and 'emotional'
Emotional might follow from tired, or it might not.
So first tackle the tired.
School is very tiring. DD2's bedtime had to come forward by 30-60 mins when she started school, and we did nothing after school at all apart from 1 swimming lesson. She couldn't even cope with stopping at the playground for 10 mins.
Just because she wasn't ready last September doesn't mean she won't be this September when she is a whole year older too, she will have much more stamina.
I would be tempted though to up to 3 or 4 mornings a week at pre-school if possible so she gets the habit of going in, and knowing you will return (to do something fun in the afternoon). But only if you think she can cope. Set the expectation that it will be fun and she will enjoy herself.
'Emotional/clinginess'. This will be worse when tired. However I do know where you are coming from. My DD2 had periods of clinginess going in to school all the way up to year 4. But she knew she had to go in and I knew that once in she was OK as busy and distracted.
DD2 used to come out of toddler ballet for hugs when 3 as she knew I was next door, but as she got older she became more able to stay.
So personally I would go for full time, but keep an eye, and if necessary take the odd afternoon out (key learning will almost certainly be done in the morning). Even if distraught on going in, chances are she will be fine. School will let you know if not.