My wife is a big gal, too. She's been using the holster from naturallyconcealed.com and really likes it, but she's thinking IWB waist rig, too.
She tried a belly band I had around the place, but it's the wrong size and didn't work out well.
I have always rejected SOB holsters, but a big curvy lady "sits differently," and she's thinking Small Of Back is worth trying.
She wore a good quality belt that I made a few years ago, and realized it will easily support a gun.
In her case, it's a J-frame S&W revolver. So now we need to learn about good SOB holsters.
Some ladies favor the "Supergirl Carry," which is lower than the naturally concealed holster, but still in front and covered by any fairly straight drape blouse on a fairly well endowed woman.
I'm off to look for reviews of SOB holsters....