How much fur shed is normal?

First time Newfie mom here. My girl, Marge, just turned one so we're experiencing the first real coat shed. It doesn't stop coming! I brush her twice a week and get an entire plastic shopping bag full of fur each time! How long does the mjor shedding phase last and how much fur lost is considered normal? This has been going on for a month now. Thank you! Pics for attention 😃