There are a million and one opinions and ways to train horses, so be prepared for a lot of conflicting opinion!
There is nothing health-wise or mental-wise that would suggest putting a saddle and bridle on a young horse shouldn't be done. Many yearlings are showin in hand in bridles so are mouthed much younger than your girl. No damage will come from putting a saddle on now if it's something you want to do.
Many people like to put basic handling on a young horse (leading, tying, picking up feet, worming, loading) and then turn them out for a year or two to grow and just be a horse with only minimal handling before they are brought back in at two, three or four to be started proper. If I had my own young horse and wasn't showing it, I would probably go this way.
Other people handle their foals up the wazoo - Teaching them everything they can, taking them for hand walks, long lining at a walk, moving off pressure, tricks, etc.
It's all up to the individual. So long as you are reading your horse and can tell if you need to back off, you will be fine.
One thing to be aware of when handling a young horse is you don't want to desensitize them too much - A bit of fear is a good thing and almost essential when it comes time to start a horse. A horse who has zero fear of humans is generally pushy, direspectful, and sometimes downright dangerous - And it often takes some rough handling by the trainer to get them back to respecting boundaries.
When are you planning on starting her?