The landlord is the only person who can evict; tenants cannot evict each other, whether they're there legally or not. This person has lived there long enough to establish tenancy, which means you can't just call the cops or put their belongings on the curb because you will be sued yourself for constructive eviction. They are not trespassing on YOUR property, they are trespassing on the landlord's property, which means s/he must be informed. However, this also puts you at risk for eviction yourself, since you moved someone in illegally.
Damned if you do, damned if you don't. All you can do is beg the landlord not to evict you, and possibly offer to pay the cost of evicting your roomate.
EDIT: She can only be a subtenant if you have your landlord's permission. Without your landlord's permission, she is just an illegal tenant. However, because it is not your property, and because she has established residency, your landlord will have to be the one to evict her.