> I don't believe you are able to donate directly as an "instead of" option.
I'm pretty sure that's not the case, at least here, as I've been personally present when a friend did exactly that.
Again, I question that what you're describing is a matter of any explicit prohibition due to policy, rather than your conclusion based on observed behavior (which, itself, can be explained by optimizing for maximum overall revenue, rather than maximum revenue to any particular participant).
To me, the split between the individual girl and the scouting organization (at troop, regional, national, or whatever level) is immaterial, because, at least here [1], the scouting organizations have routinely been in the news for their inclusive policies, even of otherwise politically marginalized girls, including putting their money behind such policies.
[1] Again, the US. Other countries may well be different.