You're right, she knows how to dress (or she has someone who knows how to dress her), but I can't help you with where she shops. What I can tell you is that she is going to have a show coming up called Kirstie Alley Big Life and they'll probably have some info in the credits.
First goal: under 180:
Second goal: 175 or below:
Third goal: 168 (no longer overweight):
Fourth goal: 160 or below:
Final goal: 145-155 (not sure if this will ever happen):