Is she scratching from the inside or outside of the house? Plus, how is she reaching the screens.....is there a ledge she has to jump to?

If there's a ledge, I'd put some pieces of double sided sticky tape or tape some scat mats along the ledge.

Here is a link that might be useful: Scat mat

A piece of chicken wire stuck in up against the screen deters my escape artist cat (who has been known to rip out screens to escape.) Of course if you use chickenwire it helps if you like the country - shabby chic look LOL.

Some other metal mesh would serve the same purpose - even temporarily blocking access would give you a chance to teach him other habits.

Which leads to my next point. You do need to provide an acceptable alternative, or the cat won't be persuaded to stop scratching where you dont want him to. ACCEPTABLE, as determined by the cat, not you! It has to be the right height, angle, have the right texture, be solid and not wiggle at all or the cat may not use it.

I've installed the pet screens, and they do work great. I don't know that I've ever seen them in any other color but black tho - I'm assuming you don't want the black? Maybe google will tell you that they do come in silver.
Never heard of a motion detector sprayer, but that's on my google list now. I have several ideas for that device.

I'm going to try the water and the double sided tape idea (if the water doesn't work). I think the scratching is mostly done when we can see her (since that's when she seems to sit on the window ledges), so I should be able to catch her doing it if I keep a squirt gun by the window (assuming my son doesn't run off with it, LOL).

Thanks!

I have a cat that scratches furniture when we're on the computer and I've learned the reason is because she wants to be fed. Seldom is it due to boredom. She only does this to the LR furniture, which is within our sight when we're sitting in the office. She never scratches the furniture when we're in other parts of the house.

Soooo......there may be other reasons why she chooses only to scratch those 2 screens.

Annz, that's hilarious, I think you hit the nail on the head. They have us well trained don't they? If I'm on the computer and ignoring Figgy's yowling and whining to be fed, he'll start picking a fight with Orange - who then starts wailing and hissing and complaining about being attacked by Figgy. Which gets me up from the computer, without fail.... Figgy never attacks Orange ever, for any other reason - they are best friends. It's only when he wants to get MY attention - too smart for their own good.

When we moved into a different house, where the windows were low and reachable by cat claw, it was evident right away that our four indoor kitties were going to scratch the screens. It meant sacrificing time lurking in the corner of one of the rooms with screens (where I would be behind the cats), but I stayed there and pressed on an alarm buzzer (the kind a woman might carry to scare off an attacker) every time a cat showed signs of interest in the screens. They learned quickly that trying to touch them with their paws would activate an unpleasant loud noise and were cured in less than a day. As I recall, I didn't have to repeat the process for all the screens in the house, either.

I don't know if this would work with cats that have already been scratching screens with impunity, but I think it's worth a try.