These are only ideas -I am not a parent, so sorry if they aren't practical.
I'd have a word with her teacher. He or she can let you know how they teach writing at the school. Tell the teacher about your daughter's lack of confidence.
Depending on what the teacher suggests I would advise following that (so that might include exercises I suppose)
Perhaps do activities with your daughter that might involve writing but also include something else (especially if she is good at it) so that you can praise her even if you are helping her correct her hand writing eg
- after a day out drawing a picture and writing a card to grandma about it
- cooking a cake and getting your daughter to write the shopping list (explain you need to help with the writing because you will shopping while she is at school, so you are checking you can read it easily),
- if you are doing a tidy up get her to write labels (e.g. for the box that has her toys, her brother's toys, the DVDs) - you can be praising her for tidying (have extra labels for mistakes)