<human>: Can you provide a brief rundown of the text in within 3 sentences?

I adopted a puppy about three months ago we named loki. I knew nothing about introducing dogs and did everything wrong. The first thing I remember was she came in and peed on Sadie (our first dog 3yrs) bed. She was sick so we coddled her, and she pushed around Sadie when she got better. 

Now I fear she is trying to become the leader, I've been training her since I got her. She knows all her basics, but on walks she tries to lead, she has never walked behind me and barely walks beside me on a good day. And now that she's older and bigger she overpowers Sadie in everything. If Sadie is walk-in ahead of her she will cut Sadie off or try to get in front of her, when I'm petting Sadie or calling her, she will sit in front of Sadie and sometimes sits on her. I push loki away and she pushes back. I ignore her and she whines. Its very frustrating because she is a big dog (boarder collie/pit) and Sadie is smaller (shih tzu/terrier), and especially on walks its gotten worse. Sadie ( who was never trained until I started about 6 months ago) is aggressive towards other dogs on the walk, which brings Loki into a frenzy. Which is bad because when Loki sees a dog she pulls and freaks out trying to greet them. Together its a shit show. I try to get them to sit and be calm, but its like the three stooges. I calm one down. The other gets up and freaks out. Any advice?
<bot>: puppy wasn't properly introduced, overpowers smaller older dog, forces herself into affection. Doesn't walk nice. Fearing she's becoming dominant because she's not listening