M.M.
Make flashcards and quiz her on a few every day.
Is she doing multiplication yet? If not then her addition facts and subtraction facts.
I used the Summer Workbooks from Barnes and Noble, Walmart has them too, but not yet. They have a rainbow on the cover and they are geared for the grades between,so it will say Summer work for the summer between 2nd and 3rd. My kids liked them. They also have grammar drills and spelling, not just math every day.
Have her bake cookies with you and double or half a recipe.
Have her give you the percentage for a tip. At first she won't be able to do it but if you teach her $3f or every $20 eventually she'll be able to do it.