At the same age, I used to work till midnight, and found it impossible to relax enough to sleep for a good couple of hours - I'd go to bed about 2/3 am and get up around 10am .I It can take a bit to wind down post evening shifts.
The problem is the gaming. For anyone, gaming from 12.30 ( or 1 by the time she gets home) till 8am is beyond wrong. I recognise you can't stay up to tell her to swtich off but this is something you need to address.It's very unhealthy- have a google about it. That length of time regularly online is very bad for your mental health.
I'd consider changing the Wi-fi password so she can't get online, and have a conversation about her finding a healthier way of winding down post work.
Re the food, sorry but get over yourself. The food in the house is presumably for the people living in the house. She lives in the house.
If she leaves a mess, address that with her, or put a plate for her in the fridge that she can eat before work the next day, or just leave her to it - and occasionally indicate to her the things that are off limits if you plan to use them for another family meal.
Your DH also has to get over himself. An 18 year old does not have to attend family outings, and for him to toss his toys out of the pram on this issue is daft. He's ruining things for everyone else, not your daughter.
So YABU, and YANBU. But you need to address the gaming.