Kathryn Erbe looks like she is around 16 in this movie...she doesn't even really have any curves yet. I just saw that she was born in 1966 which would make her 25 in this film. Nowadays she is very curvy...when the heck did she get them?
NOW I get why she looks so much older in "Criminal Intent". I was surprised how much she'd "aged", since I assumed she really WAS a teenager in "What About Bob?". But to answer your question about curves, most women "fill out" as they age, some in a very attractive way. It's part of nature, esp. if she's had any kids.