Erik didn't say he went downstairs to tell his mother. He said he was going to the guesthouse to talk to Lyle, and didn't even know Kitty was in the den.
But it's an interesting point with respect to a major flaw in the defense's story. Erik said he never saw Jose again that night. So, what happened to Jose? He'd just tried to assault Erik because he had done the one thing for which Jose had always sworn he would kill him i.e. tell others about the sexual abuse, yet this powerful man who would chase Erik to the ends of the earth couldn't find his way to the guesthouse on his own property?
Blood Brothers, page 335:
The defense was about to move into phase two of its case, when it would try to give a context to the abuses Erik and Lyle said they had endured. A series of therapists would show how a lifetime of abuse could lead to the explosion of gunfire on August 20, 1989.
But first the defense had a couple of final witnesses to talk about bizarre goings-on in the home. The first was Traci Baker, a twenty-four-year-old college student with dark hair who worked as a waitress and had a lilt in her voice that smacked of Val-talk.
She had dated Lyle for three months in 1988 and spent an uncomfortable Thanksgiving at the Beverly Hills mansion. She was having dinner one night when Jose stood up from the table and pushed his plate away. "He said something to [Kitty] like, 'what did you do to this food?' "
Then Lyle, Erik, Jose, and Traci went out to eat at a Hamburger Hamlet. No residue of anger remained at dinner, and Traci Baker found Jose to be an extremely charming man. He inspired her to go to college, she said.
Erik had referred to this incident during his testimony as a case where his mother might have been trying to poison the family. "I would normally eat the food unless I thought there was something wrong with my mother," he said.
From the way Erik described it, the family must have constantly been feeling as if their lives were in danger, wondering if today was the day Kitty would poison them all. And Jose's reaction to the threat of poisoning seemed mild. He meekly got up and went out to eat, then, after narrowly cheating death, entertained a guest with charming stories.
An alternate explanation was that Jose was being an insensitive boor by showing up his wife, known to be a lousy cook, in front of a guest and walking out on her. This kind of behavior was entirely consistent with him.
Thanksgiving was a turning point in Baker's relationship with Lyle. She and Lyle had been having sex in the mansion, and Kitty didn't like it. After dinner, when Lyle left to take a friend home, Traci stayed around and dozed on the couch. Lyle had asked her to wait for him, but Kitty came in and confronted her.
"Are you having sexual relations with my son?" she asked.
"Yes," said the startled young woman. She didn't think there was anything particular outrageous about the admission; Lyle was an adult now. Kitty's face contorted in rage.
"I've seen girls like you," she sneered. Then she told her if she thought she was going to get her hands on Lyle's money, she should forget it. Eager to leave, Baker began to rise. Kitty shoved her back onto the couch, peppering her with more questions.
Finally Traci got up, ran to the guest house, and got her things, then cried all the way home. "To this day," she said, "my self-esteem is affected."
Under cross-examination, Baker admitted she was not too humiliated to call back to the mansion later on to see if Jose could get her concert tickets to see the Who.
Here is a letter sent to Traci Baker:
http://menendezcase.mysite.com/tbakerletter.html
It is a partial, not complete, document. One or more pages are missing. The letter emerged after the first trial, and the prosecution wanted to use it in the retrial. Judge Weisberg ruled that the letter wouldn't be admissible in the prosecution's case-in-chief, but rather was material that could be used in impeachment of Lyle if he testified.
It's my firm belief that wanting to avoid being confronted with this letter, along with other known instances of attempting to suborn perjury, is the real reason Lyle didn't take the stand. IMO, it had nothing to do with not wanting to "relive the abuse," or because it would be "duplicative" of Erik's testimony.