IF her group is a tax-exempt organization, you should be able to find their finances on the internet. Some groups “watch” various tax-exempt organizations and post their findings (and IRS 990 forms at their sites. They are good sources of information. I just don’t remember their names right now but some sound like “Non-profits watch”, “Charity guides”, etc.
Google the websites using “tax-exempt anti-gun organizations”, “anti-gun organizations, and “Moms Demand Action” (they should have posted their financial status).
You can also Google “Bloomberg charitable donations”, Bloomberg Foundation, etc.
sourcewatch