Getting to know your alters is a big part of living with DID. I suggest you asking her about the situation. The body belongs to all the alters and the host. So it is a shared house. Each alter needs to learn how to respect that. Set up some rules to keep the whole house protected. If she violates the rules, then find a way to take away a priviledge such as email.

All alters are there for a reason. It is our job to figure out what that reason is.