Australorp not laying-- problem? (newbie here)

My 2 Americaunas are laying an egg a day or every other day, and I couldn't be happier-- but my third and last hen, a Black Australorp, has not laid an egg since we got her-- almost 2 weeks ago. This bird is full grown and is supposed to be a couple of years old (the Americaunas are about a year old). She may be finishing up a molt according to the lady who sold her to us. How long can a hen go without laying an egg? I swear we put the Americaunas in the coop with the nest box and they laid eggs within the hour-- but two weeks later and not a single brown egg from the Australorp.

What's her problem? Is it something I'm doing wrong? How long can a hen go without laying an egg? Do hens quit laying eggs after a couple of years? I thought perhaps they might not lay as frequently, but two weeks?

The lady who sold her to us is willing to exchange her for another bird who might do a better job laying-- which is awfully nice of her. She said give the hen another week-- which we are, of course. But, here's my second question--

Would someone look at the Chick-n-coop and the Chick-n-pen at McMurray's and tell me-- is that really big enough for 3 hens? It looks to me like it may be more comfortable for 2-- what do you think? If only two, guess which one is going back...

Advice appreciated.