things like those number 'tricks', where someone thinks of a number, and you learn a series of things to do to it, and then eventually you get back to the original number - she might enjoy working out why the various things cancel each other out
patterns of numbers on calculators - if she understands multiplication but can't yet do the bigger numbers, she could use the calculator, and see the numbers that comes up to 123456789, or 333333333 etc (I can't remember all the 'tricks' now, but I used to think it was really cool as a child).
other patterns of number - like adding up 9s (the nine times table) and how all the digits in the answers add up to nine, and make a nice pattern 0-9 in tens and 9-0 in the units
tessellation
cooking with American style cups. I remember discovering things like two quarters making a half, by seeing it on the cups, or when the half-cup measure was dirty from a previous ingredient and I was too lazy to wash it and I realised I could just use the quarter-cup twice.
which numbers have the most things that could divide into them easily. They were always my favourite numbers (prime numbers were the worst). I liked 12 and 72 and numbers like that best, because there were the most situations where nobody ever got left out (in my mind they were like groups of people, so they could be in pairs, threes, fours, sixes, etc). Also this is good practice for fractions later on, as you start to learn which numbers are good for e.g. common denominators
other infinities. What happens if you keep cutting something in half?
negative numbers - good for games where you gain and lose points each turn, or thinking of earning money/paying debts, or when you get to temperatures below and above freezing
geometry like how to build an arch etc (cathedrals sometimes have good displays on this)
Probabilities - even simple ones like a die, is it really fair? Make a chart and every day roll it 20 times and record it, how long until it all balances out and looks even? With various games, you can then get into two-dice probabilities. Like Snakes and Ladders even, how often do double-sixes come up, or whatever combination gives you some bonus in the game. Yahtzee might be a little hard, but it's good for have to make decisions based on probability, and yet there's lots of luck in it, too, so it's not like an adult has an unfair advantage either, easy to talk her through it.
Other strategy games - e.g. there's a simple one called Lost Cities - are also good for probability, thinking ahead, logic.
I used to love those logic puzzles where they give you some information and you have to make a chart and work out the rest. You know, three teachers and three subjects and three classrooms, Mrs White doesn't teach physics, Mrs Black teaches in classroom 4, chemistry cannot be taught in Class 2, etc etc. There are books of them, and they are great for the logic needed for maths. Sudoku is a similar idea, and you can get children's books for those, too.