This affects many women who permanently wear high heel shoes. The calf muscles adjusts and, over time, become so tight that they cannot stretch out to allow the use of flat shoes. Avoid this by wearing varied heel heights and do calf muscle stretches to keep up flexibility.
At Supplefeet we recommend the Yoga sandals around the house as you would a pair of slippers. these help stretch out the whole toe, foot, achilles and leg complex. Essentially they strengthen your feet, are uber comfortable and prepare your feet for tomorrows hard day wearing of high heels!
And of course look to SuppleArches the patented weight transfer inoles that I designed and keep me on my feet in comfort.