I think a co-host is like any other service you commission, you need to do your research before taking someone one on. If it was through Airbnb they only allow Superhosts to be co-hosts so this is a more suprising experience. Personally I would have tested the service before I went away.
What sort of references did you take up before using her services. Did you put a back up in place so there was someone else you could use in the event of any problems?
If you do have this co-host through Airbnb I would definitely give them a call and share your experience.
It would be a good idea if there was a review system where hosts could review co-hosts and this would be available to other hosts in your area considering a co-host.
Speak to this co-host about where you feel she didn't provide the services outlined in your contract with her (presume you had something in writing outlining expectations) and what refund you would like.
I don't know how it works in Holland but in the UK we have a small claims court that can be used for disputes like this.