I believe the story is
1. she didn't get permission and her long hair was epic
2. It made her look too much like Rena Sofer
Vanessa Marcil's 90's hair still stands the test of time so I don't even understand, but I loved her long hair. I always did think her mid 90's bob was pretty great though.
Those extensions or wigs or whatever literally take me out of most scenes. They are so awkward and I hate that some of their best moments occur with her having awful hair.
And eventually she does once it grew out a little. By the wire story she still had pretty short hair, and it was very flattering on her. I just think it was so stupid of the show to force her to have long hair.