Oh, you here!!
Well, if she's jet lagged, then sure, the night safari.
On sentosa, suggest going to mount faber to get the cable car. When you get to sentosa, you are right next to the aquarium.
Then get the "luge" down to the beach, good fun. Right at the bottom is the beach and there is a nice relaxed beach shack for brunch called coastes. You can get loungers. The beach is pretty but the supertankers are in full view!
More fun is the cafe del mar. No problem with kids if you go early.
Another option if the weather is crap or too hot is dempsey road.
Lots of brunch options, organic cafes/delis ( Jones the grocer/cucinara my favorites) and restaurants and a great indoor play area for kids with a massive padded frame.
DD can play, DH have coffe and cake and browse internet, while you get you mani/pedi. It's called GoGo Bambini (see their website)
If you want to go out al fresco in the evening and take DD along, the Robertson quay or fullerton quay or glutton bay hawker centre by the esplanade theatre are better options than the usual Clarke quay/Boat quay which are not very child friendly.
Sunday afternoon at the east coast park is good for bikes/roller blading on the beach (all available for rent) and a great seafood hawker centre for early dinner.
I imagine you must really miss them!!!
Enjoy