It depends on what information your county/city/state makes public or puts up on their website.
Outstanding warrants usually show up. But, it depends on where they are wanted and by whom. A Federal Wants and Warrants search will turn up Warrants, prisoners, and former prisoners that are in the Federal systems.
A statewide wants and warrants search will turn up the same information, but only in that State. So, to cover the entire nation, you would need to check Federal and every State.
Criminal Background Check:
Criminal records are kept by the Clerk of Courts in each courthouse. Every city, town, county, state, and the federal government have their own courthouses. We know there are 50 states, 3000 counties, and over 30,000 cities, towns, or townships in the USA. That is a lot of courthouses, and most of them do not share their information. However, it is all public information, and you are allowed to review it.
If you (or she) have any warrants outstanding, you (she) should take care of them while you are free to access your money and resources. Once you are arrested and in jail, then you have to get/pay someone else to do everything. Besides, an arrest really ruins your day/date/week, etc.