I assume that your daughter is still in the public school system or a private day school setting with the school district. She is likely in a "transition program" to prepare her for adulthood, such as learning independent living skills and vocational job tasks. If she isn't, call your daughter's IEP team together NOW. You HAVE A RIGHT to call a team meeting whenever you need to do it. You need a plan for her before she ages out of the public school system and you have no help lined up for her. I looked it up: in Utah, the student "ages out" of the school system the day before the 22nd birthday.
I found this link online for your area: http://autismcouncilofutah.org/resources/adult-services/ . The website is for people with autism, but the links on that page are for any student with disabilities. She could qualify for a lot of taxpayer support (money, job coach, group home, etc) as an adult if you get the ball rolling now. Please don't wait. The IEP team, in which you and she are members, have a responsibility to create this plan for her adult living. This "plan" can be found in her most recent IEP. The plan should talk about where she will live, how/where she will work, and what training and education she should receive as an adult.
You mention that she is "of legal age" -- do you have guardianship? There is a whole process to complete the guardianship ppwk. I wish I knew more about that to direct you to the right place. I bet the Transition Coordinator from her school would be able to answer that for you, though. If there is no coordinator, talk to her case manager (usually the Special Education Teacher).
I'm alarmed that she is taking off her clothes with boys. Where is this happening? If it is at school, you might consider asking the district to place her in a more secure, private day school setting.
Lastly, I'm so glad that your daughter's reading level is so high. Good for her! I hope that she has access to a lot of functional reading materials, such as labels, food prep directions, schedules, maps and signs, etc. Practicing in the community is a good way to apply those skills. Can she find customer service in a mall? Can she read the receipt to make sure that she was charged correctly? She's going to need to hone those reading skills for independence in adulthood.
Please message me privately if you have questions. I am a Special Ed teacher of students 18-22. I'm in Illinois, but it appears that Utah is similar with programs and processes.
EDITED TO ADD: I just read the other new responses. Someone mentioned that you should get her tubes tied. Your daughter has reproductive rights. Please tread carefully down that slippery slope. Once you are assigned a social worker/coordinator for DHS, you can ask about how this is handled in Utah.