Hi S., I just want to say "hang in there." We went through the same thing with my son when he was in third grade last year. Based on his teacher's recommendation, he was getting extra help during the school day, as well as having a private tutor at home. He was so stressed out, and complained of stomach aches all the time. However, he passed the math TAKS test and has done very well in math this year.
It seems like they have to master so many different math skills by the end of third grade (addition, subtraction, some multiplication & division, place value, money, elapsed time, etc., etc.) and it was just overwhelming for my son.
We had previously tried Kumon, which is a good resource for memorizing basic math facts (addition, subtraction, multiplication & division). Students are given simple worksheets to complete when they come in, then go home with a packet of worksheets to complete at home, so it's not really tutoring. They will start out at a level that is lower than your child needs, but will increase the level of difficulty. There is no time limit for each set of worksheets, but the student is pushed to answer as quickly as possible, and to have as many correct answers as possible. I know this works well for some children, but it just created more stress and pressure on my son.
What seemed to work the best for us was setting aside 15-30 minutes a day when possible (even in the summer) to practice flash cards, do worksheets (I buy the Summer Bridges workbooks every spring from the bookstore), or play online math games. We also play games that involve money to help him build those skils. We set goals and my son would get little rewards for reaching those goals.
Maintaining his math skills and memorizing multiplication facts over the summer helped my son be prepared for fourth grade. This year has been so much better, and he has his confidence back. It's wonderful to see him working problems quickly (and correctly!). My son now says math is his favorite subject!
I think it's very important that your daughter knows you are on her side and just want to help her so that she feels better about math because it's a skill she will need her whole life. Wishing you the best during this trying time!