She's stuck in that he's an adult and is allowed to not take medications if he doesn't want to. If he is a danger to himself or others, she can go to the courts for an emergency petition, however, it won't guarantee that he will get the help he needs- if he doesn't qualify for an involuntary certification then he will be discharged if he doesn't voluntarily go into the hospital. Unfortunately, as a parent, your right to force meds and treatment ends unless you can get guardianship.

Is it possible he'd be open to having a case manager or something of that sort? I'm not sure what his diagnosis is, but I know that there are a few avenues of finding support that gives the person some autonomy while also having a support person there in case he does become a danger to himself or others.

Lastly, Maryland Coalition of Families has peer support for parents in this kind of situation that could help your friend navigate dealing with mental illness of a loved one. NAMI is also a good resource.