Affecting her next match was only one of them; what he was really worried about was what she would likely do to herself when she found out, in order to make Tyron's plan fail.
That was the real reason he didn't tell her.
He knew her, if she knew that Tyron was going to use her, to threaten him, or even take his life, she would most likely kill herself to keep him alive!
This was something he absolutely could not see.
So after thinking again, he decided to leave it at that and just tell her about the dueling letter.
But now it seems that the dueling letter have scared her.
As he thought about it, Jake suddenly also regretted for telling her about the dueling letter.
If he had known, he would have simply kept it from her all together.
But he knew that there was no way to hide it from her, she would find out sooner or later, and when she did, she would probably blame him for not telling her.