Stand up for your beliefs, and only say yes if you really want to.
One reason why the fairies are so happy is because they're assertive with each other. This trait is very different from aggression, which denies the rights of others. Assertiveness, in contrast, honours everyone's rights (including your own). Assertive people are easy to get along with because you always know where you stand with them. Your current situation calls for you to be assertive: Speak your truth with love; and let go of unhealthy, old communication habits.
Read books or take a class on assertiveness.
Don't do anything out of guilt or obligation.
Be a good role model for others by practicing this trait.
Say no to this request.
Be true to yourself and your values.