They can get information from her. Much more so than they can get from a single Sending spell. It would be way easier to just scry the place, sure, but that doesn't work because of the Cloyster. So rescuing someone with info is a valid strategy, specially now that infiltrating a new team would mean building the whole "resistance" infra-structure from the ground up again.
They're "wasting" an easily renewable resource (spells) that would probably go to waste anyways (unless we assume every idle wizard finds a way to burn all of their spells every day) to get potentially important information. That sounds like a fine trade, to me. In fact, it sounds like an effortless way to get an edge on your enemies. And, assuming Team Peregrine's view on goblinoids is any compatible with the elven government's, Gobbotopia is their enemy, the whole deal was not just a way to help the Azurites.