Difference between frictional unemployment and seasonal unemployment
What "seasonally unemployed" means? 

First, to be "unemployed", one must actively be seeking for work, as the OP stated. The adjective "seasonally" here would reflect the fact that Julie is looking for a seasonal job, and couldn't find any. But this information is not provided to us. Irrespective of her past employment, Julie may have been looking for a permanent job, in which case she should not be categorized as "seasonally unemployed".