Ezio, you did leave out a important information: did you keep "the apple" during the interrogation, or not?
There are roughly two ways to play that scene talking in character, and you can go back-and forth from one or the other when you want during the scene.
The first one: you have something very specific in mind, you only need someone (who can be Manuela or not, but usually in the "without the apple" dialog there is no reason to having the principal played by another player) to "play the character", reacting to what you say. In this case Olga can cry, can shout, can tell you "no, please, stop" or anything Manuela think it's appropriate to her character. She could, even, add something more substantial, but this is tricky, you have the apple, so anything she says is subject to your veto. You can say "no, she does not do/say that" to anything she say. By the other hand, Manuela is the principal's player, so she has the same "veto power" on anything you want her character to say.
Tricky, as I said: it can work for longer scenes if you two are really on a roll, and play on each other's cues, but the longer it last, the more the risk of having some veto stopping the flow. I usually use that mode for very short bits, when all I need is the principal's reaction to something another character says or do. Then I pass the apple.
The second one. You talk in character, say what the character you are playing says, then pass the apple. The next person can play anybody he/she wants, even the same one you played before, or he/she can play Olga, say something, then pass the apple.
This is not so "blind" as it seems: when you do it in play, after a while you see that Manuela says what Olga says of substantial, and the other people at the table play everything else, from people to the weather, and the apple is moving from person to person so quickly that you can begin talking, pass the apple around, and finish yourself the line of dialogue after the apple has made the entire round, three seconds later.
There is a example right in the first thread I linked from the Spione furum:
Michele: "Issam's home. Horst knock on the door, he is with a a guy wounded by the police" [point at moreno to pass the buck]
Moreno: "Issam, help us! Oper the door" [point at Claudia to pass the buck]
Claudia: [frame Valzyna's first scene]
Michele: "Issam open the door and let them enter" [point at moreno to pass the buck]
Moreno [play in Vanzyna's scene]
Claudia [play in Vanzyna's scene]
Michele: "Issam let the wounded lay down on the couch, as look at his wound" [point at moreno to pass the buck]
Moreno: "the wound is very bad. If this man will not be cured in an hospital, he will die" [point at Claudia to pass the buck]
Claudia: (playing Horst) "can you save him? Please, Issam!" [point at Michele to pass the buck]
Michele: ""Horst, we need to get him to an hospital, or he will die!"[point at moreno to pass the buck]
Moreno: (playing Horst) "We can't go to an hospital! The police is searching for us, he shoot a policeman!" [point at Claudia to pass the buck]
Claudia: (playing Horst) "Issam, you MUST cure him here, it's the only way!"
Claudia [out of character] do you want to enter flashpoint?
Michele: "Yes, but not to convince Horst. I want to save the wounded here"
Moreno: "OK, so from now on, you can't add nothing to this scene until we go to flashpoint.... but I can! You hear police sirens outside of your house, and remember the trail of blood leading to your door..."
Claudia [laugh]
Michele: [groaning] "thank you very much. Let's make Vanzyna go to flashpoint very fast, Ok?"
[...]
The entire scene was played in character. Issam (the principal) was played only by Michele, as you can see. Me and Claudia together played Horst, taking turns in talking for him, and used the times we had the "apple" to add concrete elements (the wound is almost lethal, the police sirens approaching, etc.)
This way, you can play even very long scenes, with a lot of characters, without having anyone dominating over everything. You only have to learn to say "yes" to each other's contribution. Maybe you wanted to play Horst like a cold experienced man, but you pass the buck/apple and the next player make him drop on his knee crying. No matter. Go with the flow. When it's your turn again make him cry even more (or maybe it was a ruse and he is only playing a part?). If someone add something that you really can't live with, go to flashpoint as soon as you can and use your cards to cancel it.
How that scene would look, played in the fist manner, the one I talked about before, with someone keeping the Apple the entire scene, for fear of "losing control"?
There was an example even of that:
Michele: "I would like to frame a scene in Issam's home. He is resting on the couch when Horst arrive with another radical, wounded in a fight with the police during a demonstration. Horst is desperate and ask for Issam's help."
Moreno: "Issam, help me, we need a place to hide!
Michele "Horst, what are you saying? You can't hide here! You will get me in trouble! And who is this guy?
Moreno: "A friend. He is hurt, please!" - and, changing tone to indicate that he is talking out-of-character "do you want to enter flashpoint?"
Michele: "No, I let him enter"
Michele: (in character): "try to avoid ruining my carpet with the blood"
Moreno: "thanks, Issam, I told him that you could help us, that you are a good friend!"
Michele: "yeah, yeah" ...
Michele (out of character) "Your turn"
Moreno: "you check the wound. It's worse that you thought. If this man will not be cured in an hospital, he will die"
Michele: "Horst, we need to get him to an hospital"
Moreno: "No way! they will arrest us!
[...]
Notice as (1) Moreno (as Horst) doesn't tell, during Michele's turn, anything that isn't already stated in the narration or in the framing of the scene. He simply react, without adding anything substantial. He is simply playing color, somebody for Issam to talk to. and (2) Claudia is not playing. There are only two characters in the scene, played by Moreno and Michele, they are playing a conversation, and she has to wait her turn without any character to play. (OK, she could play the wounded, grunting and moaning...)
Remember that you can jump from one way to the other anytime you want, even in the middle of a scene: all you have to do is stop passing the apple. But it's better to avoid doing so for too long, as you can see in this manner you are only asking the others to help you stage what is really a monologue. Role-playing works better as a dialog.
[edit: crossposted with really a lot of people...]