Protective ~ Feisty ~ Cautious
Beatrice is motivated by Hiro. She's motivated to protect her, in a sense. She's very close to Hiro, which makes her want to watch over her, in a mother-type way. Hiro's mother isn't mentioned in the story, which could mean she doesn't have one. The same is true for Beatrice. Beatrice sees this and automatically fills that position for Hiro, so she still has a mother figure, unlike herself. She knew how it was not having a mother and she didn't want the same for Hiro, so she took that position. Towards the end of the story Beatrice orders Benedick to kill Claudio. This shows that Beatrice loves her to the point she would have someone murder the person who hurt Hiro.
Through most of the story Beatrice rejects the idea of marriage. She constantly denies that she'll ever fall in love. Although she says this, she's actually insecure. "Your Grace is to costly to wear every day" (Act 2. Scene 1. Lines 321-322). This was her reply to Don Pedro when he asked if she would consider marrying him. She felt that she wasn't good enough for him. She also broke up with Benedick because she was afraid of rejection, but by the end of the story she overcomes these insecurities. This is shown when she agrees to marry Benedick.
Beatrice has a great impact on the theme. She shows how love can be painful and make you insecure. But she also shows that you can overcome them when you find someone you really love. Beatrice also adds to the plot because of her relationship with Hiro. Without Beatrice, Hiro would've probably acted differently since Beatrice stood as a mother figure for her. Also, Benedick never would've been order to kill Claudio, so there would've been no conflict between those two and it would've lessened Benedick's importance to the plot and theme.