Thanks for sharing! I went back myself to book 2 book 3 being a step up again from two. So far book two gives you a good foundation to changing chords and alternating. I know what you mean with feeling disheartened at times. But breaking down parts , like practicing only difficult measures, like your teacher recommends is what I do now too after hearing another music teacher saying that. I am slow as well but stopped comparing myself with others... unless it's great advice such as all these different replies here!
Moving slower might be just good practice as well. I rushed through book 2 but enjoy now to memorise my favourites from it. They are still a challenge