Playa Mujeres is a super safe gated community. There are two levels of guarded doors, so basically once there you'll only see the guests and staff. The same thing on the beach, without vendors, etc. The journey from the airport is a bit varied, but by no means dangerous, as long as you book a reputable car service.
An employee who answered the phone at the hotel said the shooting occurred on the beach near the facility. Several cartels are fighting for the area's lucrative drug retail trade, including the Jalisco cartel and a gang allied with the Gulf cartel.
Playa del Carmen is a generally safe destination for solo visitors, though they should be careful, as misdemeanors and scams are known to occur in Mexico. Just as the Hotel Zone is made for tourists, all of Isla Mujeres is also made for tourists.