A Downingtown driver multiplied the risks of causing casualties when she got behind the wheel in April with a cell phone in hand and a small plastic bag of marijuana for delivery, authorities allege.

"The facts of this case are extremely disturbing," Chester County First Assistant District Attorney Patrick Carmody said yesterday. "It's fortunate more people weren't seriously injured."

Police said Meghan L. Obendorfer, 18, was exceeding the speed limit on rain-slick Creek Road in East Brandywine Township about 4:30 p.m. on April 14 when she failed to negotiate a curve and slid into the path of a school bus in the opposite lane.

Obendorfer's passenger, Nicolette Pomon, 17, of Downingtown, who was nine months pregnant, was pronounced dead at the scene; a certificate of fetal death was issued to Lillian Grace, her nearly full-term baby daughter, police said.

Steven Dilworth, the driver of the school bus, which did not have passengers, was treated for minor injuries, police said. Obendorfer was treated for injuries at the scene and at Reading Hospital.

Obendorfer, who is free on unsecured bail of $25,000, is scheduled for a preliminary hearing Monday. Her charges include homicide by vehicle, reckless driving, and marijuana possession. She and her attorney, Glenn E. Davis, did not return calls seeking comment.

Carmody said he hoped the fatalities would generate action to prevent such tragedies in the future.

"Personally, I think Pennsylvania should follow New Jersey's lead and ban the use of cell phones in cars," Carmody said. "We have a younger generation that is dependent on cell phones and texting; it's unrealistic to expect people to do that while paying attention to the road."

State Police Superintendent Frank E. Pawlowski said his department supported such a ban.

According to 2008 PennDot statistics compiled with state police data, a driver's use of a hand-held cell phone was considered "a contributing factor" in 1,049 vehicle crashes, six of them fatalities, PennDot spokeswoman Alison Wenger said. Hands-free devices contributed to 50 crashes but no fatalities in 2008, she said.

Wenger said the numbers are likely underreported because they depend on eyewitness accounts or evidence that is not always available.

According to the criminal complaint, East Brandywine Township police found two cell phones, one of which Obendorfer had been using, and a small plastic bag of marijuana in her 2007 Chrysler PT Cruiser.

Phone records showed that Obendorfer received 39 messages and calls in the hour preceding the crash, the complaint said. Text messages indicated that she was making a drug delivery to a female juvenile in Glenmoore, that she had a conversation with her mother, and that she was in a hurry, the complaint said.

A draft text message to the Glenmoore girl was started at 4:30 p.m. and was not completed, the complaint said.

Accident reconstruction showed that Obendorfer's average speed was 43 m.p.h. before the impact with the bus, the complaint said. The posted speed limit is 35 m.p.h.

Contact staff writer Kathleen Brady Shea at 610-696-3815 or kbrady@phillynews.com.