I just wanted to let you know that I think that is completely normal behvaiour. If she was crying through the day, I'd be worried, but at 13 months they *all* cry at separation. Those who don't are the exception. If she's easily distracted out of it, with a cuddle and some playdough, it is normal (although hard!) and she will be OK.
There are kids out there who still cry on separation at 4 or 5 after being in care from 6 months! They are fine most of the day, and it's a fairly healthy reaction from a child who has a good strong relationship with their parents.
So expect the brief episodes to last for a while. If she's crying when you arrive, then I'd be a little more concerned.

As for school holidays.... I don't know the best solution! Not that I claim to have all the answers, but after 9 years in childcare I am pretty cluey about what works, and honestly, the jury's out. Some children's behaviour doesn't change too much after 2 weeks off, and some have a real struggle. From my position, as a caregiver, I feel like I lose a lot of ground in my own relationship with the child in that time, so feel like I'm going backwards sometimes. But on the other hand, some kids come back SO chilled out after two weeks with the folks that it's great to have them back.

Can't give you the answer, I'm sorry! But I hope you feel a bit better about it all.