Dog barking is getting worse

[Tinytigertail]

My lovely girl is a mixed breed rescue. She is aged between 7-9 and over the last year or so her barking at anyone walking past the front of our house has increased dramatically. She's often in the room on her own, so it's hard to 'catch the moment' to distract her. Short of keeping her out of the room, does anyone have any ideas on letting her know that she doesn't need to react?

Privacy film on the windows.

The only way to train her really is to be in the room with her on a regular basis so you can usher her away from the window when she barks and give her a reward when she doesn't. You could also try shutting her out of the room when she does it. It takes time but she'll get the message.
Dogs only do what they're allowed to. If they aren't stopped they don't know it's wrong.

I'll second this. I have it on my windows. It's great. The dogs don't react to people walking past and nosey feckers can't see in.