Who calls it a pistol? Is this the old west. How in the hell did she get a gun? If one is being treated for mental illness are you allowed to have a gun? Seems like a bad idea to me.
Yes by both Federal and State law it appears legal
Federal
https://www.atf.gov/firearms/identify-prohibited-personsNV
Nev. Rev. Stat. § 202.360.
A person shall not own or have in his or her possession or under his or her custody or control a firearm if the person:
Has been adjudicated as mentally ill or has been committed to any mental health facility by a court of this state, any other state, or the United States;
Has been found guilty but mentally ill in a court of this state, any state, or the United States; or
Has been acquitted by reason of insanity in a court of this state, any other state, or the United States.