Stubborn fat is stubborn for a reason; primarily to do with hormones, catecholamines, receptors and blood flow. In women, as you know, it's usually the hips and thighs giving the biggest problem. Sound like for you it's the belly and upper back... which isn't unheard of either.
I used Lyle's SFP after I did a PSMF to get pretty damn lean and SFP worked quite well. Is it a magic formula for spot reduction? Fuck no. But I think it helps more than anything with stubborn fat for people who are relatively lean to begin with.
Outside the realm of Lyle's methods in that book, there's nothing I know of. I mean you can tell someone to keep dieting, then diet some more... eventually the fat has to come off, right?
The SFP is for women who are in the mid teens in terms of bf%, which sounds like you're close to.
In my experience it's wrong. I mean I'm talking seriously lean here, not your average member here, but the few people who desired and I've helped get really lean proved to me that some people are more genetically inclined to have abs and others aren't.
Even myself... I've gone down to single digit bf% and my abs are never glaringly obvious as in a magazine shoot. They're no doubt there but not how I'd imagine it.
Given that you already follow a low carb diet (right?) I think SFP would be your best bet.