How does Lina add risk to her escape from Ember in Chapters 15-17 of The City of Ember?

In Chapters 15-17, Lina adds risk to her escape from Ember by bringing her baby sister Poppy.

When Lina and Doon discover the underground cave providing the means of escape from Ember, one of Lina's first thoughts is how she will manage to bring Poppy with her. Doon discourages the idea, however, reminding Lina that Poppy will be safe with Mrs. Murdo until the rest of the population of the city can join them. Lina concludes that she is indeed "only being selfish...to want to have (Poppy) with (her)" (Chapter 15).

When the day of their planned escape comes, however, circumstances do not turn out as Lina and Doon have planned. Instead of welcoming news of the two children's discovery and making plans to save the city, the mayor has sent his guards to pursue them, and during the Singing attended by all the citizens, there are repeated blackouts worse than any that have occurred before. In the midst of all the confusion, Lina is forced to make a precipitious decision, and she chooses to bring Poppy with her after all (Chapter 17). Although she knows that bringing a small child along on their dangerous and unknown journey will provide added risk to her and Doon, she feels that she must bring the child because she has come to realize that

"there is no safety in Ember. Not for long. Not for anyone...Whatever happens...now, it's better than what's going to happen (in Ember)" (Chapter 18).