I judge dressage and will give up the day I upset a child on a Shetland (also a new mother hence the hour!).
It's encouragement all the way at that age - however just install in her the 'do your best' mentality and she'll be fine. Dressage judges are human (I do wonder with some though). It would depend on who is in the class as to if I would higher my marks or not although I do tend to generally give higher marks if it's a very novicey or childrens class - it means they are all marked on the same level but aren't all getting 3's and 4's. Obviously you can't do this affiliated but I do with unaffiliated I don't want to put them off before they start.
Call for her if you want (even if she knows it she will be nervous) and if she goes wrong it doesn't matter - the number of kids and adults who burst into tears is very upsetting!
Remind her she's only really competing against herself in dressage - if mums have to run in and help then so be it.
Most people lose marks on the use of the arena - easy marks that let the pony down so use of corners - riding to letters - shapes of circles. Even the stiffest of ponies can bump their marks up if a test is ridden accurately.
The only thing I would say is make sure she is turned out correctly - I am a stickler for it and it is so easy - I'm sure she will be if it's pony club but gloves, no bit rings etc and neat hair in hair net if needed - I hate hair flapping about.
Tell her she's meant to enjoy it and it's 4.5 minutes of her life! Which test is she doing OP?
Happy to answer any other questions you may have.
Tell her good luck!