Discuss with a local attorney who handles guardian and probate matters. Every State has different standards, but you will need expert testimony, more than likely from a doctor to get her involuntarily committed. I am adding tags to your question, to help you get advice from attorneys who do this type of work.
You will need to start with a physician who deems her incompetent. After that you can then go to court and be appointed Guardian of her "person" and her "estate".
Please consult with a local attoney who handles adult guardianships so that this is done properly. If you file a petition for guardianship and are appointed your daughter's guardian, you will have the authority to seek help for her. Your lawyer will instruct you to get her to a doctor who will state that she is not capable of handling her own affairs due to her illness. There is a specific and not difficult Report of Physician which must be completed.
Hi, It is unfortunate you experiencing these difficult circumstances. In Illinois, you will need to search out an experienced Mental Health Attorney if you are seeking to involuntarily place her in a mental health facility; as guardianship powers do not reach that issue. If you fear for her safety and the safety of others then you should immediately contact the local police to see if they will take her to a hospital for a mental health evaluation. If two physicians agree that she is a danger to herself or others they can hold her for a hearing on placement. Do not delay. Protect your family. You can use the search function here on Avvo.com to find an attorney who practices in your county.
Of course, as always this answer is general in nature, applies only to Illinois law, assumes certain facts omitted from the question and does not take into account any facts specific to any person’s particular circumstances. No attorney/client relation is created hereunder and I highly recommend you seek first the counsel and advice of an experienced contested civil litigator prior to taking any actions relating to this matter, as seemingly insignificant actions may have unintended consequences.