CAMBRIDGE, MA (CBS/WBZ) - An Irish nanny has been arrested and charged with assault and battery in connection with the death of a Cambridge infant. The accused entered a plea of not guilty and bail was set at $500,000.

The neighbor of Aisling McCarthy Brady has some harsh words for the Quincy nanny now accused of violently abusing an infant girl in her care who later died.

The 34-year-old hid her face in court as prosecutors detailed the case against her; the diagnosis for injury abusive head trauma very violent shaking or impact.

And today, we learned Brady was here illegally. The Irish citizen overstayed her 90-day tourist visa back in 2002. Betty Davis, founder of In Search of Nanny, Inc. says, "Parents need to understand this is the most important decision they can make."

It's not known what the baby's family did or did not do in their search for a nanny, but local experts say a background check would have been essential. Davis says, "It just sounds to me like this person wasn't screened because supposedly there was some background there."

Brady's recent history includes at least two restraining orders and assault charges against her, some stemming from bar fights. Davis says moms and dads must learn as much about a nanny's history as they can. She says, "Of the people that I've interviewed and screened for parents who just have me do that, probably 40 percent something happens, or something comes up."