Aliens: Dark Descent

There's 7x queens in total in the game. 4x of the Queens you encounter you're required to kill to advance the mission, there's 3x that are optional (at least one is missable).

Missions with required Queen encounters: Mission 1 (Dead Hills), Mission 5 (Pioneer Station), Mission 6 (Atmospheric Processor 27), Mission 11 (Olduvai Dig Site).

Mission 2 (Berkley's Docks): towards the end of the mission, you're required to go into her lair to retrieve an item, this can be done through stealth and you can avoid triggering her. You'll return to this level later and maybe able to engage this queen once you've levelled up but I haven't tested this.
Mission 8 (Tantalus Research Station): after unlocking the underground base, you'll work your way through it and you'll come to a terminal that unlocks a lot of the secured doors (there's also a camera terminal that for the use of an engineering tool will show you the queen's location on camera). As you make your way towards the objective marker, there's a corridor with 3x locked doors that you can unlock (using the terminal next to them) that will let you engage the queen. You cannot return to this queen after completing this mission.
Mission 10 (Pharos Spire): This Queen is outside and at the back of a building on the south of the map and can be engaged relatively early in the mission. It will pop up as a secondary objective to investigate as you proceed through the mission most likely. She's in a dead end and you can lay a trap for her, move forward to wake her up and then kite her through a minefield.

Queens are tough and you can't always get time to set up turrets etc, especially in mission 5 where you're forced through the door in a cutscene. This, in my opinion, is the hardest one to fight.
My best advice is to use suppressive fire to slow them down and if you have any, set up turrets before hand (don't be afraid to reload the save as it'll let you prepare before encountering). If not, keep hitting her with grenades if you see "charging" or if she does a grab attack on one of your marines as it's an instant kill.
Once I'd progressed enough in the game to unlock a lot of the specials, RPGs and plasma rifles etc, Queens aren't a challenge as long as you prepare, even on Nightmare.