R.R.
It's a Christ-centered character development program dedicated to the mission of building young women of integrity through service to God that has only been around since the mid-90's, it began right there in Ohio. It's kind of like apples and oranges, you really can't compare them. If you're happy and content with your daughter in GS, that's all that matters. You're free to choose what your daughter is involved in, as are your niece's parents. I wouldn't be concerned what they think.
AHG focuses on a Christian environment to teach girls and help them to grow, basically God is first and foremost in everything they do. They generally include all age groups in one group to teach the girls to work together, so it might not work for parents of a 5 or 6 year old to have their daughter be in the same group as a middle or high schooler, but it has the advantage to families of allowing sisters to participate in the same group. They focus on good citizenship through service, and must do a minimum of 3 community service projects a year. Perhaps that's what your brother or BIL meant about the cookies, that they should give the cookies away rather than sell them, I don't know.
I will say, having been a Girl Scout for many years and loving it, the past 3 years I've been accosted by tween girls trying to sell cookies in front of supermarkets, who tried to guilt me into buying their cookies, while a mom stood by and allowed it. Different stores, different moms and daughters. I've said something to the moms in prior years, who basically turned their back on me or tried to argue with me, so I get where the girls got it. When it happened a few times this year I ignored the girls, while the moms looked on wild-eyed as I didn't respond, as if to say, "How dare you!" I've found the copycat recipes for all the cookies and have blogged about and pinned them all, I won't ever buy them again. And this is coming from someone who used to fill a freezer with them to have year-round.
Girl Scouts is way different than it was when I was a child and teen. My leader wouldn't have allowed or encouraged us to behave as some now do, she kept our troop service-based, I had her the entire time I was a Brownie to a scout in HS. My daughter didn't want to participate in GS because of how some of the girls acted and I didn't force her. I wish we'd had AHG to at least try.