Depends on the school. For example at Duke you need to meet with the dean of your dept and get approved for leave, then when you’re ready to return you need to show them what you’ve been doing in your absence to get approval to return. At UCLA IIRC there’s no real process, you just don’t register for classes the next quarter, and when you’re ready to return you just sign up again. So quite a big gap there, with probably a lot of variations in-between.
My DD had no “curfew”…but then she got into a minor car accident while driving late after dropping her BF off at home…now the car has to be home by midnight (or she can stay over). She has gone out later but had someone drop her off.
If marijuana is illegal in your state then state that you don’t want illegal substances in your home.
She is not an adult - age alone does not make her an adult and honestly she is acting very much like a child; wants all the privileges of her age but uninterested in the responsibilities. You and your husband have to get on the same page.
People with sleep problems sometimes resort to using substances like pot and alcohol in order to sleep better. However, pot and alcohol use are known to cause sleep problems. A viscious circle! As others said, a job or volunteer work can help structure her life right now. Sometimes a cure for sleeplessness is having a job that requires you to get up early. A couple of exhausting days can put you on a normal schedule. If not, there are non addictive options. Good luck.