This model isn't consistent with the specific reasons McGonagall gives for the prohibitions she does specify. She talks about liquids evaporating, recolored hair falling out, inanimate objects undergoing tiny internal changes that affect the original form.

Even if McGonagall knew how to safely do what she did, she shouldn't have used that example in a safety lecture. A student might try Transfiguring something into an animal, and might include the fact that animals breathe in their visualization of the target form.