Why did Ella and Char search the castle in Ella Enchanted?

Ella is looking for Lucinda to help her get rid of the curse, and together with Char, they arrive in Giantville. There, they see that the giants are treated practically like slaves, and Char promises them that once he becomes king, they'll be treated fairly and equally. Together, Char and Ella and some of the giants celebrate, and Char and Ella share a romantic moment.
Char then suggests to Ella that they should go to the castle's library and look for some books which might help them figure out where exactly is Lucinda. Thus, they decide to spend the night in Giantville and go to the castle the next day. Once there, Ella searches through the library and manages to find some useful information about Lucinda's location in Benny's book, while Char tells his uncle Edgar about the giants' situation and informs him of his intentions to marry Ella.