Re BBM
When its their turn in a trial, either side (Prosecution or Defense) can call whatever witnesses they want to the stand. So if the Prosecution decides they do not want to call her to testify, then when its the Defense turn, the Defense could call her up to testify and then the Prosecution will likely want to question her during their "cross-examination" of that Defense witness to try to repair any damage from her testimony that the Defense pulled out of her.
Some trials are fascinating to watch and this one is setting up to be a doozy of a trial. There is so much strategy and tactics involved for both sides, it can get very interesting.
My understanding of the main trial proceedings is the Prosecution always goes first to present their case and they will call up all their witnesses one by one. During each witness testimony, the opposing side can elect to "cross examine" (question) that same witness right after the other side is done with their questioning. This continues until all the Prosecution witnesses are called up to testify.
Then its the Defense turn.
The defense begins calling all their witnesses. And the same holds true that the Prosecution can elect to "cross examine" each of them after the Defense is done with their questioning.
So if a certain witness is not used or called up by the Prosecution, then it doesn't necessarily mean that the witness will not eventually be called to the stand by the Defense. And so the Prosecution needs to be ready with how they will question her during their cross examination of her. They can elect not to call her and not to do any cross examination of her if the Defense calls her, but usually its to their benefit to at least cross examine a witness if a lot of damage was done to their case by the Defense turn with her.
The bottom line for either side is they will usually call a certain witness if the benefits outweigh the disadvantages.
The strategies and tactics by both sides can get really interesting and dicey at times. Some of us have watched trials and others have seen enough from movies and documentaries to have seen some of the tactics that are employed. One of the things an attorney does is they try to bring out the testimony from the witness that they want the jury to hear and they try to limit the witness to just answering the question they have posed to them. A lot of times a witness will want to add more to the answer but they are promptly cut off by the attorney if they are fixing to say something the attorney doesn't want the jury to hear. That can happen and especially if a witness is considered "hostile" to the side. The attorney will tell the witness to just answer Yes or No and they will cut them off as the witness tries to add more if it hurts their case. That is where the other side can help themselves by cross examining that same witness and then they can bring out the extra information that the other side did not want the jury to hear.
It is all very interesting and quite a chess match in certain cases like this one is shaping up to be.
All JMO
Criminal Trial Overview - FindLaw