Whoever says potty training a dog is easy is either lucky or they know what they are doing. The problem is your dog is very young at only three months old and she needs to toilet every few hours. Even after three months you might not be successful in your efforts to train her.
Even though you have done all the right things, such as crate train your dog, put the dog outside after a nap, teach her toilet training outside, and maybe tried other things as well, but still it is not working.
What do you do next? It is at times such as this when you wish you could talk to her, and she could understand the behaviour you want from her, then the problem would be solved. But she cannot, so stick with it. Communication between the two of you is really the key here.
You need to know what the correct procedures are that ensure success, that is the link that is missing.
If the potty training still is not working for you, here are two things you can try.
1.Leave her outside after she has toileted to have a sniff around, rather than bring her straight inside. By doing this you are telling her being outside is for fun and not just for toileting.
2.Keep from playing with her until she has toileted. That way she will want to get it out of the way quicker so she can play with you.
Good luck with the potty training.