I mention 10.6 mHz because that is surely a big clue to this problem.

I have a client who has a shot at getting a low power station, from thirty miles away, KKJZ, KJazz, the best jazz station in the United States, at 88.1. Trouble is, she is in the hills near the transmitter for 98.7, Arrow FM, KMediocre. She gets interference like mad from the closer station.

Why is 10.6 mHz an issue? The IF frequency is probably 10.7 mHz, as it has been since frequencies first started being modulated, and the interference is probably just the original station frequency leaking into the second stage of the tuner.

Anybody have any idea how to attenuate a narrow range of FM frequencies? I am not about to start doing research on building traps....

Ernie, You only need a handful or parts to build a notch filter and get rid of the primary offending frequency on FM. If you are getting interference into the IF range, well the choices would be to do some modifications inside the receiver with shielding or get a different receiver. I would try a different receiver.
All of the good receivers I own have at least one tunable notch built in. ICOM and Yaesu over here. IC-R9000, IC-756, and FT50R.
Don't want to build one... [Link: universal-radio.com]

ft7600....[Link: winegard.com]

The name Yaesu makes me think of communications receiver, not Consumer Home Theater Audio/Video Surround Receiver. Names like Marantz, Yamaha, Denon, Sony, etc come to mind. I have never seen any user adjustments on any of those sets. Since at least 1970. If the Yaesu is a type of communication receiver, hell, it might even have a BFO! But that won't help this client.

Ernie,
I only listed the communication receivers for reference to ones that have great selectivity and adjustable notch filters that I own. I did not mean for your customer to own. You could use one though.
Most decent communication receivers are great for antenna tuning, partly because they have signal meter.
The tunable Fm Trap filter I listed should be your first attempt to fix the problem.
Why didn't you list the receiver in use with the problems? Maybe someone else here has similar issues.

Wow, if that isn't something I have written a hundred times!

Because I do not remember the model number. It is a fairly recent Yamaha. She had it when I started the install, so I can't check my sales book to see what it is.