By definition, the victim's cooperation is needed for a court appearance. But the victim goes through various stages: she loves her pimp, she does not love him any more, she sees qualities in him, and so on. With young victims, especially very impressionable ones, it can be difficult.
But there are some quite extraordinary programs in Quebec. With Mobilis, for example, all the social services in a youth centre join with a police service in an attempt to make the victim's testimony and care easier. Everyone says that it all comes down to the way victims are looked after. If they have good support with them in court, if they are not left by themselves, they will testify against their pimps.