Looks like she is about to cry in every scene????

I'm not exactly sure but Melanie Griffith was battling a drinking and cocaine problem at the time. They even had to halt filming the day of the wedding scene because she was so intoxicated and high. She went to rehab after this film and as she has said "It saved my ass". This info can be found under her profile in the trivia section.

There's also the fact that her life was pretty grim and going down hill fast. On the same day she found out her boss was lying to her and stealing her ideas and that her boyfriend was cheating on her.

The character was probably suffering from depression. Whether this was due to Melanie's acting, drugs, or both, who knows but it seems to fit.