Ok, that's a field I'm not familiar with. I guess this is more of a government field of work and they are more conservative in their hiring process. I found the following jobs and the amount is pretty limited (and in Eastern Germany/Saxonia): https://www.xing.com/jobs/hydrowissenschaften?keywords=Hydro... or https://www.melioplan.de/stellenangebote

Edit: https://www.stepstone.de/jobs/wasserbau-ingenieur Here are far more jobs, so there seem to be at least some available.

Did she contact some professors at her university here in Germany? They often can provide contacts to industry or the government.

Other than that good look at finding a job for her, she should not give up!