Okay naman na itinerary mo.
If you're asking for additional na pupuntahan, it might be difficult to squeeze it in your current iti.
But i noticed you didn't include In your current iti yung other famous landmarks of Singapore like Gardens by the Bay and Merlion Park. Unless you've been there before then never mind.
For other parks naman, since you'll be staying in the east side, your sis probably knows East Coast Park. But usually one afternoon ina-allott dun for biking, rollerblading, pwede mag-ihaw (have to book in advance), picnic, hehe. Or eat at Jumbo Seafood.
About sports outlet stores. You'll be staying near the airport diba? There's one nearby. It's at Expo Stn, Changi City Point yung name ng mall.