Go, Bailey.
Technically, a dog has not fully mastered the command until she only performs it on request. When she does it without you asking, she is "throwing" sits at you (which is very common). Once you are confident that she recognizes the command you give for Sit, you should not reward her for unrequested Sits. Otherwise, she'll try it in front of you when you're carrying groceries.
I would introduce one trick at a time, returning periodically to ones she already knows to keep it fresh in her mind and build her confidence. Remember you want to "set her up for success", so don't make it TOO hard for her.
Usually people teach Down by putting the dog into a Sit, and then luring the dog's nose down with a treat.
The classic way to indicate the wrong behavior was given is to look away and do nothing for about 5 seconds.
Keep us updated! It must by nice to have a smart dog.
