Hi, I'd like to help you with your question.
If your girlfriend used any type of hallucinogens during her years of drug use (either on purpose or by someone else giving them to her without her knowledge), then she most likely is suffering from drug induced psychosis. This is basically brain damage caused by the use of these drugs. The drugs affect an area of the brain called the temporal and frontal lobes. It affects a person's ability to reason and can cause all the symptoms you describe.
Your girlfriend's lack of insight is also another symptom. A person with a severe mental illness does not see they have anything wrong with them. They feel that what they believe is different and they are special. Or they just don't see that there is a difference at all.
Preoccupation with religions or religious beliefs is common with mental illness but harder to differentiate. Though it is ok to have faith (a person may believe that God loves them without ever seeing God, which is faith), but when the faith becomes a way to explain someone's different point of view or symptoms, then it becomes a tool rather than faith.
Many of the people suffering from psychosis or other severe mental illnesses become involved with cults so that may be why you are coming across this information as you try to research her symptoms.
If you can, try getting your girlfriend to a therapist for an evaluation. She may refuse because she does not believe she has any problems, but it is worth a try. She could also see her regular doctor (though they are not trained to diagnose mental illness they may know enough to help) and he/she may be able to help do a preliminary diagnosis. The doctor could also try to encourage her to seek help, maybe even referring her to someone in particular. The doctor could also order an MRI or other tests to see if he/she can determine if this is drug induced psychosis.
One of the best ways to help your girlfriend is to educate yourself and her family about having a family member with a mental illness. Here are some resources to help you:
When Someone You Love Has a Mental Illness by Rebecca Woolis
The Burden of Sympathy: How Families Cope With Mental Illness by XXXXX XXXXX Karp
Helping Someone with Mental Illness: A Compassionate Guide for Family, Friends, and Caregivers by Rosalynn Carter and Susan Golant M.A.
You can find these books on Amazon.com or your local library may have them for you.
Although you may not be able to force her into treatment, you can try to influence her to seek help and get answers. You can also support her and her family to help her live the best life she can.
I hope this has helped you,