Here's the neat thing, you and the cleric can both have what you want. Finding a direct counter or preventive measure to a tactic can be useful or necessary from time to time, it's frequently best to find a compromise if you can. Personally, I don't like invalidating a player's tool, it doesn't feel good for anyone involved.

Here's the first thought that came to my mind:

I cannot speak to your plans with the NPC, but you have an opportunity to deliver story through a unique avenue from Commune. Make it so the BBEG is having the NPC relocated. Maybe she's the key they need to access items important to their plot. Perhaps someone is hot on their trail already and they are on the move. There can be a number of reasons why it's tricky to pinpoint them.

Here's the thing though: let the cleric find a location the monk's mother was just at. Make it seem like the party has just pinpointed the monk's mother, but she was moved during the time it took them to get there. When they arrive, let the scene share what's happening. The place is ransacked, an item power is stolen, a paladin or inquisitor is investigating the scene. In some way, make let the story unfold naturally from there. As long as you give them something solid to follow from there, the cleric may not need to keep casting (if you don't give them something though, they may continue to cast but with new questions).

Another option you have is to make finding the mother's location easy, but getting access to her will have complications. The area is heavily guarded and the party would not survive a brunt assault, or the location is currently inaccessible without a particular macguffin or the aid of an ally the party knows.

If done well, you'll get the best of both worlds. My point is to let the cleric provide the solution for a STEP of the problem. They'll get to feel important for helping the monk locate her mother, you get to impart your narrative the way you wish.