Apologies if this sounds harsh - you have let it go on for 2 years, it is going to be tough to get her our of this habit.
First thing I would do is shut her door, and also put some sort of gate accross it, like a stair gate that she can't open.
You also have to be really strict, and whenever she gets up, take her straight back to bed, withou talking to her, except to say, its night time, time for bed. Don't get into any arguments, or conversations, it is her way of delaying. Make sure all the other doors are closed. Maybe even put bolts on the downstairs doors out of her reach so she can't open them.
Try a reward chart. For every night she stays in her room (even if she wakes up), she gets a tick or a star. For every time she is out of her room, she gets a cross. At the end of the week if she has all stars, or way more stars then crosses she gets a treat whether it is a new toy or book, a trip to the cinema, special outing with parents etc. Also try not letting her do things like going out to play with friends "because she is too tired" from not sleeping at night.
Ask her if there is anything in her room she doesn't like, or something (within reason) that you could do to make her happier there.
Good luck.

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