My wife is the same way. I thought she was bullshitting until the day we had a friend over. He'd just gotten his medical card and wanted to make edibles. We did a whole southern spread with neck bones, collard greens, and cornbread. The cornbread had a gram of live rosin in it. My friend and I ate one piece and were nearly comatose (I was high for a day and a half), she had 3 pieces and didn't even get a buzz.

Apparently some people's liver metabolize THC too quickly for edibles to have an effect. (I tried to find a real source for this but only got results from companies that sell stuff so take this with a grain of salt)