By David DeKok

HARRISBURG, Pa. (Reuters) - A 14-year-old Pennsylvania girl has been charged as an adult for allegedly taking an active role in the stabbing death of her mother and plotting with her soldier boyfriend to murder her father, a prosecutor said on Thursday.

The teenager and Caleb Barnes, 20, plotted the murder of Cheryl Silvonek, 54, via text messages and mobile phone calls, Lehigh County District Attorney James Martin said. Both are charged with homicide and conspiracy.

The girl's lawyer, John Waldron, said 14 is the minimum age in Pennsylvania for trying a child as an adult for murder, and his client just turned that age in February.

The slain woman had ordered the couple to break up after she discovered the boyfriend's age and found out he was having sex with her daughter. Text messages released in court papers portray the teenager as pushing Barnes, a soldier stationed at Fort Meade, Maryland, to carry out the murders.

"She threatened to throw me out of the house," the eighth grader wrote to Barnes in a text message on March 14. "I want her gone."

A juvenile witness overheard the teenager plot the murder of both her parents in a cell phone conversation with Barnes on March 7, according to court papers.

The same witness also heard her discuss her father's life insurance and who would gain custody of her if her parents were dead.

The mother reluctantly drove the couple to a concert in Scranton on March 14. Barnes allegedly stabbed her to death when they returned to the Silvonek home in Orefield, Pennsylvania, just west of Allentown, early on March 15.

They buried the body in a forest about two miles from the house, but while they were doing so a suspicious neighbor came out and saw the blood inside their car and called police.

Police later found the car in a pond but traced it back to the Silvonek house. They found the young couple naked in bed, according to court papers.

They did not attempt to murder David Silvonek, the teen's father, according to the papers. The pharmacist was asleep at home at the time his wife was slain.

(Editing by Frank McGurty; Editing by Sandra Maler)