What about a musical instument? That would lead to a discussion of fractions (whole note, half note, quarter note, dotted note, etc.; also e.g.,3/4 time), patterns, and things like that in a less-obviously mathy way. Also, when I learned to play the piano, I thought of the keyboard as a number line with middle C representing zero and the white keys as whole notes and the black keys as decimals, and it really helped me to form a visual sense of numbers.
Another thing that might be mathy but not obviously so would be time. What about getting her a watch of some sort and then just incorporating discussions of time into your conversation during the day? For example, how much time until meals or particular events, how much time it takes her to get ready in the morning, how long a t.v. show is compared to a movie, or really anything.
Another thought would be origami, although she's young yet and may have trouble with the fine motor skills.
What about going on hikes or bike rides with a pedometer or bike computer and figuring out steps over a certain period of time, or elapsed time, or how long it takes to walk 50 steps up a steep hill vs. on a flat surface? You could also time her running different distances.
Or you could try simple sewing projects together that would involve measuring and cutting, size scales, etc.
I think I would attempt to compliment her subtly on her good figuring skills, but I could also see that doing that would call attention to the fact that she was doing "math" and that could end her enjoyment of the activity, so I guess I would play this by ear based on her personality and reactions.
