Hard to say what was really bothering her, it could have been the saddle or it could have been her excited about the other horses and as soon as they were out of sight calmed down again. Someone else may have better insight.
But when it comes to tightening the cinch, you should be able to fit 2 fingers snuggly between the cinch and your horse's belly. Some people tighten it up more than that at first because they are expecting the horse to puff up and hold its breath a bit.
Some formal lessons will be a good idea, the more sources to learn from the better.