Yes it is possible for some to be able to as you call it call up alters. its called co consciousness. co consciousness is when a person knows their alters exist, can hear their alters can communicate with their alters and can share their experiences...

examples of co consciousness.... feeling like an observer while an alter is in control. one common documentation with DID is when people who are DID have reported that they have felt like a back seat driver. or felt their alter take control so they slipped backwards...

those rare few that I was co conscious with it felt like being under water calm and quiet but hearing words come out of the bodies mouth that did not sound like me, knowing what was happening when an alter was in control.

some people that I know have a deeper level of co consciousness where they are able to talk inside to their alters and ask for an alters help. like in one situation i was getting overwhelmed by an alter's feelings. i was able to think to that alter that I was ok, that I needed to do this and to step back, let me handle things. though that alter was not too happy about it they did step back so that I could continue to talk with my treatment provider.

some people (its extremely rare ) have the even deeper sense of co consciousness where they can think inside to an alter and that alter will step forwards. if you type into amazon the words DID I'm sure you will find many great books that document such events as this. you can also talk with your treatment providers. they can explain how this deeper sense of co consciousness can happen.

here in america its unethical for treatment providers to "call out" alters but it is not illegal or unethical for one to "ask inside" to their own internal system when they feel they need the help of their alters.

Again its extremely rare to have this deeper co consciousness level but it does happen. More and more people are reporting things like being a watcher while their alters are in control, being able to communicate with their alters.....knowing when and who is taking control and what is happening when the alter is in control so much control and less than marked discontinuity that the American Psychiatric Association created a new diagnostic label for this....Other Specified Dissociative Disorder and Unspecified Dissociative Disorder.

this person in the show may have received her diagnosis before the new diagnostic labeling went into affect and who knows some people are using the new labels and other people feel more comfortable with the old labels.

before may 2013 all people with dissociative type alternate personalities were called DID regardless of how much control \co consciousness they had.