If you've taught her to accept the blanket already, that's very good. First, I'd start simply by grooming her. If she accepts being groomed all over her body, then start with a saddlepad; let her sniff it, and when she's finished sniffing it, rub it on her neck a bit, then offer for her to sniff it again. Rub it all over her body; shoulders, hips, back, even legs a little. Periodically let her sniff it, then place it on her back once she's calm about all of this. She'll probably turn to look at it, but otherwise be calm. Once she's used to this, you can get the saddle and let her sniff it, and place it on her back.
Next comes the cinch; let it down, then switch to the other side, reach under her belly, grab it, and buckle it snug; don't tighten it at this point. Also, when you reach for the cinch, don't duck your head to look for it, Keep your head back and watch her foot; if she kicks, it'll be in a safer spot, and you'll have at least a tiny warning.
Let her stand there for a little, and tighten the cinch 3-4 times gradually. If you pull it tight right away, she'll associate the saddle with sudden pain and will start fussing and fighting when you try to saddle her. The same thing will happen with a bad fitting saddle, but that's something I'm just learning to do myself for the first time; currently, I ride bareback while I look for one.
When you unsaddle her, don't unbuckle the cinch and drop it; use the leather piece you buckle it with and lower it slowly. If you drop it, it could hit her leg and startle her or, worst case, bruise her leg. Lift the saddle off, don't just drag it off; the stirrup will likely slide across her back, but you want the tree to lift clear; this again will help her not spook. Also, don't ride her the first time you put the saddle on; get her used to doing groundwork with the saddle on before you ride her.
