3 monthss is not too early. But to train her to go outside, you need to teach her to go out side. You go to the door and take her outside when you think she needs to go (several times a day) EVERYTIME she goes outside then praise, praise, praise, and treat. Act happy, jump around, do the potty dance, it will work. Patience and consistency are the key. You can start with the bells right away also, just hang them on the door or right next to it, and ring them the first week or two that you start the outdoor training. Then, gradually introduce her to them, just put her paw on the bell so it rings before you go out, then proceed with the pottying. Keep doing this and she will pick up on it. Yorkies are smart!!! My AprilLove is now indoor pad and outside trained, and she uses the bell. She also rings the bell when my other 2 outdoor trained dogs need to go out or come back in!! It is so cute, she started doing this on her own!! Be patient and it will happen. But keep repeating every day. Also it is good to have her walk with you to the door, don't carry her there. Hope this helps and here is a link to a little clip of AprilLove letting her Bcihon brother Bailey in from the outside. (You can see him standing outside the sliding glass door) I was able to catch her doing it then told her to do it again just so I could show my sister how good she was!!hehe cause she didn't believe me.
http://www.dropshots.com/day.php?use...0&ctime=181338