How is lying a theme in this story?

Through the character of Liz Buxbaum, the novel explores how telling lies can be costly in relationships. Lies are troublesome, especially when one begins to stack lies on top of lies. Liz Buxbaum is a high school senior who tells a couple of lies and discovers the damaging effects.

Liz's first lie is a lie of omission to her best friend Jocelyn and her stepmother Helena. Liz and Jocelyn are seniors, and Jocelyn has been looking forward to sharing the typical senior milestones with Liz. This includes a day of shopping for the perfect prom dress, but each times Jocelyn suggests a time for the shopping trip, Liz comes up with an excuse. Meanwhile, Helena has hinted that she wants to be included in the trip. What Liz does not tell either Jocelyn or Helena is that she is heartbroken because her mother – who died when Liz was in fifth grade – will not be here to share this event. Both Helena and Jocelyn have hurt feelings as Liz continues to make up excuses or ignore the hints to include them.