What kept that temporary employee from seeking a permanent position?Why should he? It's a temporary job.
A temporary job that lasts four yeas is "temporary" in name -- and for the employer's convenience -- only.
Oh, yeah -- nothing.
This is a ZOO. It is almost impossible to get a job in a zoo as a worker. Zoo, marine center, museum, anything like that. Volunteers work there for YEARS without ever getting hired at all. She's lucky. She should either shut up or leave and let someome else have the job.