I just looked up the biscuit recipe from the above book and I think . . .
If you are using her recipe but the weather is not humid you will need more buttermilk, maybe a couple of tablespoons.
When I bake biscuits, always buttermilk biscuits, I find that I get a better rise if I make a wetter dough. You don't want it pourable, but you for sure need it wet, wetter that I think the above dough would be. And don't over handle it. I don't even roll my out any more, I just pat them out evenly and then cut with a biscuit cutter. Since the dough will be wet, don't be afraid to use plenty of flour on the board and on the dough itself to knead (gently, gently about 5 times) pat it out and then cut.
And PREHEAT your oven well! If you have a baking stone,heat it while preheating the oven, place your pan/tray of biscuits on it to cook. Good spring in the oven when well preheated and cooked on a HOT stone.