This is pretty much the same thing they are demanding from her - we don't want your password, we want access to your hard drive.
As I stated in my comment above, in the case of properly encrypted data where exactly one person possesses the key this is not the same.
If the court decides that encryption is like a safe then, regardless of how impossible it is to open the safe without a key, the court can coerce you into decrypting your HD.
However, if the court decides that encryption is like a secret language that only you can translate (a more accurate representation of encryption, in my opinion) then they will likely rule that they cannot coerce you into decrypting the data.