Actually BfoD is (partially) correct. While Liz was supposed to be boyish, Fey herself displayed a fair amount of (very fine IMO) cleavage in a number of episodes
, often with Liz wearing a moderately low cut shirt under her blazer.
Basically, Liz/Fey was an example of that old TV trope
where the "ugly" character is actually a knockout. Everyone talked about how plain she was but objectively she had a very pretty face and nice, curvy, body.
That being said, I think Fey's talents extended well beyond her looks.