"And you've got the faith that I could bring paradise." The one thing Gemma Tonks hadn't realized upon the engagement of her brother and Andromeda Black was that her family was now a part of the Tonks's - including Sirius Black, who loved to show up at their flat beaten and bruised.
After witnessing the death of her family, Teddy looses all hope of living. Placed under the protective care of the Potters and with Sirius Black becoming her literal shadow, Teddy has no time to willow in self pity. Not when Sirius wants her to fight.