Although passwords are new, combination locks are not. There is a lot of case law on this.
http://www.google.com/search?q=5th+amendment+combination+pas...
"In distinguishing testimonial from non-testimonial acts, the Supreme Court has compared revealing the combination to a wall safe to surrendering the key to a strongbox. The combination conveys the contents of one's mind; the key does not and is therefore not testimonial. A password, like a combination, is in the suspect's mind, and is therefore testimonial and beyond the reach of the grand jury subpoena. "
Edit: Why it matters in this case: FTA "the government seized an encrypted laptop from the home she shares with her family"
The government cannot prove that the laptop is hers. If she provides a password, and it works she has proven that the laptop is hers, and further that the contents are under her control. Therefor the act of provided the password would be testimony.