Get Moving!
Grab your best bridesmaid and take a walk, go for a jog, just get outside and move! Think of it like a social event! A chance to bond and talk while you get fit together! Plan on meeting up 2 or 3 times a week, after work, on your lunch break, or early in the am. No excuses! You don't want her to bail on you, and you can't bail on her!
Even just walking can make a difference in your body, your mood, and your friendship!
Or...
Boost your walks with bursts of energy and adding some small friendly competition: "I'll race you to the end of the block!" or "Let's sprint the rest of the way home!"