By the time a young man or woman reaches 18 years old the legitimacy of ADHD as a diagnosis tends to be much lower. Simply said, the symptoms you describe here are related to worry and anxiety and that is not the primary symptom(s) of ADHD.
Indeed, the symptoms are in line with a worry type obsession.
And the medications that she is taking may actually be causing some of these symptoms if not exacerbating it. These medications do not work the same way in many people as we age and mature, and in teens this medication can even cause people to believe things that are untrue. Even the manufacturers website that I just reviewed states this.
If this was my daughter I would do two things. I would immediately have her seen by the doctor who prescribed the Vyvanse. (Even if she does have ADHD there are other choices.) I would be very clear that she has developed an obsessional type worry and that she needs to be reevaluated for a different medication. To encourage you, Some ADHD medications work on serotonin, which reduces worry and should also help with her impulsivity issues.
All in all this seems like a medication reaction due to either poor tolerance of the medication or simply her age and the nature of how this medication works. I would also encourage her to seek support at community mental health agency as the treatment is often free or low cost, and she can see a counselor and a psychiatrist (or a different one) and receive the emotional support she deserves as well.
There is more than just hope here. She needs a medication reevaluation to smooth things out and that is where I would start. With that, I can see you having a great chance of seeing the old 'Sam' Steven
Yes I do as even the manufacturer acknowledges that this is a possibility.
The medication does impact the prefrontal cortex, and it tries to improve that area of the brain's ability to control impulsivity. Overstimulated, which is the possibility I think you are seeing, you get obsessional worry and bizarre beliefs.
Easily corrected if this is the case. Steven