TMZ has learned that medics responded to a call at the Residential Reentry Center Tuesday afternoon for an "unspecified medical complaint." We're told Abby was able to walk out of the facility on her own and got into an ambulance, where she was taken to get care.

Sources close to the situation tell us Abby is currently in the ER at a nearby L.A. hospital. It's unclear what her issue is at this time.

We broke the story ... Miller was transferred from prison to the halfway house to serve the rest of her time for bankruptcy fraud. When we last saw her, she was looking happy and healthy getting her nails done.