If one has to write cod-medieval adventures with the depressing parts of history toned down (and someone must: I read so many that if no-one else did, I would have to), I am mildly sympathetic to the over-representation of princesses. The Tough Guide to Fantasyland might explain why princesses were under particular social constraints not to act independently, but I can see throwing in a currently-believable spunky princess and getting on with the adventures.
(As I write this, I am losing my sympathy, because even if one has to have a royal character why can't she be a queen? Children in adventure stories are disproportionately orphans, and an orphaned princess should be a queen. Older brothers are rare, unless minions of evil, which ought to remove one from the succession.)
Both Poison Study, by , and The Decoy Princess, by , do not need princess-dom. They're nearly redshirts. The first heroine learns palace intrigue from other servants and soldiers, and the second is brought up as a princess but turns out to be a tethered goat for assassins; in both cases they have time and reason to practice suitable skills for going off and having exciting adventures.
And, in both cases, they turn out to actually be the princess-equivalents in, basically, magic ninja societies. These characters did not need to haul around that crutch. Oh, well.
Find in a Library: Poison Study, The Decoy Princess, or Tough Guide to Fantasyland.
So wrote clew in SF&F.