So for the shock of the explosion to force the saucer into the planet's atmosphere, Troi would have had to deliberately position them between the drive section and the planet. She simply could have flown... gosh... away from the planet.
I don't see this as a biggie. We witness the saucer getting only a very short distance away before the core blows - it wouldn't make any difference if some other course were selected because the saucer would in any case still be sitting right next to the stardrive section, not having been able to make the course choice "count" yet.
OTOH, plunging into the atmosphere might be a valid tactic for protecting oneself from a nearby warp core explosion. That's the only "shadow" available anywhere near the kaboom, after all.
As for turning away when you are being pummeled... What could possibly be wrong with that? Turning doesn't detract from Riker's ability to fire back (except with bow torps, but we know that those can't be used at close quarters anyway - only Klingon Birds of Prey ever fire torpedoes point blank, and those green things never make a big bang like the Starfleet photorps), and it gets the wounded and still vulnerable throat of the ship away from the Klingons' line of fire.
Having Troi pilot the ship through the battle doesn't lend itself to excuses, though. Sorry.