The big recital takes place at a more formal venue than mini-recitals, with a larger audience capacity. This is a really great event to invite friends and relatives to- it’s the “show off” recital for the year!
There is no dress code for the big recital, but dressing up is encouraged. It is more important, however, to be comfortable (in terms of nerves) than to be dressed up- so if a dress or uncomfortable shoes also cue the jitters, go with the familiar.
In general, I require students to have had a chance to perform before the big recital: either a mini-recital or at a minimum a group class. Usually for very young, nervous, or inexperienced players it is best to attend a group class for a performance and then a mini recital, until there’s a level of comfort with smaller audiences. This makes for a more successful big recital experience.