If she was meant as sorta the latest person Picard taken under his wing (since Ro, Wesley, & Data were cited). Guess its Picard's choice to pick the whiny, bratty, pain the @$$ personality type this go around.
Mage, I get your point about being versatile, I suppose Chen is dabbling too much and becoming the Jack of All Trades/Master of None. Worf had several years to move around. Chen's hardly been around (it may be years in Trek Lit, but really she's only been featured in a handful of books)....and yeah going from Contact Specialist -- to Captain's aide to being a VERY JUNIOR officer in command of the ship, is just a big pill to swallow.
Yeah, she may be the Officer of the Deck at the time when she took command, but really there shoulda been a more senior person on the ship (LT CMDR or CMDR). There wasn't the need for ALL the senior officers be on the planet's surface), and when the bulk of the senior guys are down below, there SHOULD Be a senior guy as Officer of the Deck.
Trust me, on an aircraft carrier or destroyer US Navy ship, you may have an LT as the Officer of the Deck, but when serious shit is happening, you have more seasoned guys....and if you have an LT during serious shit, you have an LT with LOTS of experience bridge experience.
In regards to switching roles...I still annoyed that Kim is now security instead of Command track or Enginneering or sciences. When has he ever even MENTIONED a desire to be a security guy. And then he is the HEAD of Security, AND leads some ground attack....PULEEZE.
It like the US Navy guy in charge of security on an aircraft carrier is helluva lot different than conducting some ambush.....and even if someone had those skill sets, I doubt, he'd have been PRIOR to that working in Engineering/Sciences for awhile all while being an Ensign/LT...but Kilm was sent to Seucrity for plot device....it just even MORE BLATANT with obnoxious CHen.