In the library, Bianca was bored waiting for GoldMiner so she had moved a chair from the library and placed it near the secret passage. She sat near the secret passage, guarding it while she was reading a book.
Bianca could have searched the library instead of waiting here for GoldMiner. However, she believed that there wasn't anything useful in the library anymore.
At least a fourth of the library was already searched by Bianca and GoldMiner yet they didn't find anything aside from the secret passage. Guessing that there could only be one game item or clue in the luxury cruise ship's entertainment facilities, Bianca didn't search for more.
After all, it was also risky to search for more since she would be distracted in doing so. If she was too focused on searching the library, there was a high chance that she wouldn't know what happened in the secret passage.