Poor kittythehare! You sound so frustrated. I really feel for our Irish friends trying to follow. I could only say that this all seems normal to me as far as the court proceedings. The judge is the expert on the law and trials, so he knows in his mind what is allowed and will limit both sides to a narrow focus and interpretation of the law that goes to the heart of the case arguments.
For example, the Prosecution cannot bring up prior convictions that have no direct bearing on a case. But if a defendant takes the stand for the Defense, then that "opens the door" for the Prosecution to bring up any prior convictions and prison sentences.
For MM, if she took the stand, the judge might disallow her prior psychiatric history because she is claiming self-defense from an assailant and MM is not claiming diminished capacity or insanity. OTOH the judge might decide to allow such information as generally indicative of her state of mind, character or good judgment.
The judge will not allow the Prosecution to create any unfair prejudice against the defendants which is likely underlying some of today's disallowed testimony or exclusion of any certain evidence. In the USA everyone has an absolute right to self defense. The State must prove that they are guilty of more than self defense. The judge denied the Defense motion to dismiss, so he is saying that the Prosecution has met the burden of the prima facie case that this MAY be second degree murder, let us proceed.