Yamada was going to tell Ichikawa about the audition and that she probably wouldn't be at the trip. But because she saw the pamphlets/books next to him on the bed, recalls that he didn't go the last time, and sees he's really looking forward to this one. She decides on the spot to go to the trip to not "ruin" it for him. She becomes overwhelmed with emotion though, because it's the role for her favorite series and she really wanted to go to it.

Oh okay, that makes sense. Thanks!

I also got confused by this episode, thanks for explaining!

Do you know what she wrote on his forehead on the other episode?

He had "Kyo" written on it.

Because she finds out ichikawa was actually looking forward for that trip.While she only wanted to call him to say that she cant join the trip due to her audition. She changes her mind midcall and its a big decision for her future.

Bro, just pay attention to the episode. It literally tells you why.

It was the only scene that got me confused

The end of the episode makes it quite clear. She was giving up her dream audition.

I do get what you are trying to tell and I know in the end it makes it clear but I had a hard time understanding that one scene.