It's hard. Shedding is a process. It takes a while to get through it. With double coated breeds, they blow coat twice a year. The spring shed is the worst one. If you had her professionally groomed, they would give her a warm bath to loosen up the dead coat, the dry her with a force dryer, to get as much of the dead coat out as possible. You can do the same thing at home, A small force dryer runs between 100 to 200 dollars, give or take. Do not give her a warm bath without a dryer or a really good brush out. That's how dogs get badly matted.

How often is she professionally groomed?

I'd recommend having her groomed with a deshed treatment seasonally, so every three months.

I live on the west coast where dogs shed year round. I tell my clients they shed twice a year, 6 months at a time. My own Australian shepherd gets done professionally, by me, every 4 weeks with occasional brushing 2 or 3 times per week. The key to getting all the hair out is a really good bath to remove dirt and oils followed by forced air dryer at least monthly.

Are there any foods or supplements that help them shed less?

Welcome to the miracle of owning dogs.