Angela is a human-fish mutant that makes a brief appearance in Maximum Ride Forever. However, she is not seen in any other books.
Before Maximum Ride Forever
When Nino Pierpont first brought the Flock to Paradise, she and Nudge swam at a waterfall along with some of the other mutants.
Maximum Ride Forever
Shortly before Rizal officially takes Max, Nudge, and Total as hostages, Nudge recognizes Angela and waves to her; however, she doesn't wave back.