A CRJ-50 First Officer described receiving an APU oil pressure caution message that triggered a divert since they were already operating with only one aircraft generator available.

Narrative

Climbing through FL190 in VMC; the APU oil press caution message came on. I was the pilot flying and said; 'I have the radios.' The Captain ran the QRH checklist and advised with the APU required because of the #1 generator being deferred; we would have to land at the nearest suitable airport. We discussed our options for airports and decided on the best choice. The Captain notified the Flight Attendant and Dispatch of our situation and I told ATC that we would need to divert. They asked if we required assistance and the reason for our diversion. I explained that our checklist required us to divert to the nearest suitable airport for our configuration. They asked if we were declaring an emergency. After discussing it with the Captain; informed them that we were not at this time. Captain spoke with the Flight Attendant several more times and gave her the needed information before we landed. The APU shut itself down after we landed as it said it would in the QRH. Sometime while being vectored ATC declared the emergency for us because CFR was waiting for us at the airport. As we taxied into the gate; a ramp agent knocked on the door and the flight attendant opened the door before we shut down the #1 engine or turned off the seat belt sign. After shutting down both engines and confirming we were chocked; Captain called Flight Attendant up to say she should have waited to open the door. I got up to see the passengers out. I noticed that Flight Attendant was upset and crying. I asked if she was OK and she replied 'NO'. While up in the waiting area at the gate after the flight; several passengers said we had done a great job but were concerned about the emotional state of our Flight Attendant.