Start just by exercising with her!
Lifting her up in the air over and over is not only totally fun for her, but great for your arms.
Strapping her in a front-pack now, a backpack later when she's bigger, or a jogging stroller, you can go for a nice walk with her... if it's dark already when you get home, is it possible to find a track where you can go? Maybe at the high school?
Don't push yourself super hard but just go for a walk! It will be good for both of you.
On the weekends, if she's big enough to go in a swing, push her for a minute and then run around the swingset. Repeat. Believe me, I have done it... it helps if you don't mind people looking at you funny, haha.
Dance around the living room with her in your arms. This is cardio AND playtime.
Right now she is your primary focus, so if you figure out ways to be active WITH her, you won't feel like you're neglecting her to work out. And if you start small, hopefully you won't be too exhausted.
Good luck! I know how tiring it can be... mine is 16 now though
| current weight: 130.0