Welcome to the forum BB.These dogs are very stubborn and strong willed and that is why they are not for everybody. It takes a person who is more determined and a strong personality to dominate the dog (without violence) and make sure that the dog know that it isn't in charge and you are. There are so many different methods of training and each dog responds differently. If you go to the TRAINING section of this forum you can find many posts that cover different approaches. IMO, one of the very first posts to read and method to try is NILIF. This has worked for countless people. You can go directly to the post by clicking HERE
I am glad that you realize that it is you who needs the training too. These dogs want only to please you and get your affection. The difficult part is being able to make the dog understand what you want it to do without confusing it. Once they know what you want they will do it, well, most of the time, LOL.
Also, do keep in mind that Stella is getting into her terrible teens. This is a period when they seem to have forgotten everything they learned including their training. She'll grow out of that.
We would enjoy you starting a new thread in the INTRODUCTION section of the forum telling us a little about yourself and your pup and some pictures of Stella. We really enjoy pictures here and the more the better. Best of luck and feel free to ask question if you can't find the answer in the search feature.