What about miracle grow brand potting soil?

I've been using it. My plant looks nice. It's about 1 1/2 months old. But do you think using only potting soil will work? It supposedly feeds for up to three months. And with transplanting, new soil gets added. Should I at least add a little sand and maybe some clay to retain some water?

You'll get a descent plant with potting soil only (though nutes will increase your yield). If you decide to re-flower the girl, you'll need to buy nutes.