I've been a substitute at the same school over 10 years and I work mainly with grades 1-3.
Many children get frustrated because they see someone else finish before they do, etc.
We use a lot of math manipulatives to help them learn. Examples:
Last week we used 2 pennies and made a chart of how many heads or tails we had on the chart and counted them.
Dice game.. use the number you roll then decide "how many more" (we've done that with how many more being 100). You could always scale that down to 20, or a number she would be more comfortable with.
Play 21 with playing cards.
They LOVE Fasttmath on the computer.
We always do at least 1 multistep problem a day with the UPS check Explain method. Understand, picture, solve, expain your answer.
Fill in missing numbers on a chart, greatest to least, etc. A lot of activities that reinforce the knowledge of where numbers are placed.
Parents can help out by having her count how many apples to purchase and weigh them, etc.
We aslso practice with large magnetic coins to identify them and what th value is, then we will post some on the board and say how much?
I think you are on the right track making it "fun" to learn the basics and concepts and then she hopefully will find it "fun" to solve the problems.
Good luck to you!