Okay, like we often say when we read these things: "There's got to be more to it than this."
If this really was the first incident, it seems the next appropriate step would have been to dismiss MR. Birch from the rehearsals. According to the article: "Ms. Birch’s contract had called for her to have a bodyguard, and Mr. Birch said that he was serving that role because 'Thora had had some stalking issues in the past.'" So they could have said "okay, fine, but you have to sit outside the door, or it has to be someone else" and they'd still be within the contract. So the fact that they so abruptly fired her... There is something else going on.
(As the Stage Manager, if they've got it in the contract there's not really a lot we, or even the director, can do - we can't kick him out. But we can/SHOULD report to General Mgmt/Producers, ie. the people to negotiated the contract, about the disruption to the process he is causing).
I've had actors with parents as managers or agents and never had this problem. (on my show with children, the parents are not allowed past the stage door for any reason.) I've also had actors with stalkers and while we made some accommodations, never had a bodyguard IN THE REHEARSAL.
I guess my bigger concern is the fact that this "woman" is TWENTY-EIGHT years old and she can't handle herself or her daddy. Sounds like Dad has some major control issues and Thora has some major passivity or dependence issues.