I mean, it's pretty obvious the easiest way would be for her to move out asap, but unless you're willing to chuck her out, the only thing I can suggest is chilling out and taking a step back.
I'm not really sure why some of those things bother you? If you mean her bedroom light is on all night, who cares? How does that impact you? She can obviously sleep through it (sounds mad to me but up to her I suppose), and modern light bulb costs about a penny an hour to run for 8 hours so even if she does leave it on all night it costs you about 50p a week.
Same with her food -. If she's left a mess and gone to bed, go and wake her up and get her to tidy it, but other than that if she's just left it packed up but not in the fridge, just leave it. If she gets food poisoning, again, not your problem. It's not going to kill her. If she doesn't get up in time for work that's her issue, and for her boss to tell her off, not you.
Why do you do her washing and ironing? If you don't, she'll have to wash her clothes eventually. Perhaps she doesn't see the point of ironing (I don't). Either way, there's no reason you need to do it.
Yes she's behaving like an overgrown teenager but you're treating her like one! Ideally she would grow out of it, but after more than a decade that doesn't seem to be happening, so if she won't change her behaviour the only alternative is changing yours.