Quick Summary: It sounds like you're having some basic challenges so no worries, we'll get you back on track in no time.
If you prefer Gris over Hirge, by all means stick with Gris. She's my favorite companion. Maybe after a few levels, and more experience with the game, give Hirge another try but it's totally okay to stick with Gris. Her tank and combat ability might help you out.
It sounds like you've hit the stretch in the game I call the limbo. The early game is pretty easy, but the mid-game stuff is just daunting. Stick with it through as the limbo only lasts a few levels. Some extra gear, some extra traits, and poof you're doing well again. Note: The limbo used to be a bit longer but a game rebalance helped shorten it.
So on that note, give this a try:
You have access to the fire pit in the tower so make that your focus. Get you Gris, get some fire resist stuff (rings, those goblin shoes that drop in the mine, and fire resist potions). AND CAPS FOR CLARITY: Fire damage is only reduced by fire resist. So keep an eye on it. Fire potions are helpful. Maybe pick up a few Giant Strength potions from Jabel for Gris (that +6 damage is nifty).
When you take on the fire pit, clear out one room at a time. It might be useful to tell Gris to "Wait here a moment" and than lure out or two enemies to you, and run back to Gris (ideally around a corner). That might help you survive the first few rooms.
When you reach the end of the hallway, be mindful of those pesky flames. The fires will heal fire imps, and do constant damage to you. So either bum rush them to overhwhelm them (will take heavy damage), or try to lure them out. If you leave Gris way down in the hall way, you can tell her "Wait here" and "Attack only those that are near you". Than you can lure the imps and wolves away from the fire pits.
Clearing the fire pit will net you a Fire Mace that can be used by Gris and Hirge.
Lastly, trolls can only be killed by fire damage. The killing blow must have fire damage. You can damage a troll with non fire weapons, but if the killing blow doesn't have a fire damage aspect, the troll will regenerate.