Tell me it gets better

Today is day 4 with what the shelter called a Aussie/Border Collie mix. She’s 4 months old. She had such a sweet and gentle disposition at the shelter. Now that we’ve been home she is reactive to everything. Dogs on the tv, her reflection in the glass, the sound of someone moving down the hallway, cars driving by. She’s a leash puller. She squeals in the crate that she willfully goes into. I just don’t know what to do. I am willing to put in the work, I just don’t know how much I am going to be able to train out of her. Tell me it will get better 😭