Here's my advice: Work through each of the texts listed below. By "work through", I mean understand all proofs and do most of the exercises. This will bring her up to speed with roughly the average junior math major at the average US college. Note that prerequisites parenthesis.

1. Simmons, Precalculus Mathematics in a Nutshell
2. Axler, Precalculus: A Prelude to Calculus (1)
3. Stewart, Calculus: Early Transcendentals (2)
4. Velleman, How to Prove It: A Structured Approach (2)
5. Boyce-DiPrima, Elementary Differential Equations (3)
6. Ross, Introduction to Probability (3)
7. Axler, Linear Algebra Done Right (4)
8. Niven, Elementary Number Theory (4)
9. Herstein, Abstract Algebra (4)
10. Apostol, Mathematical Analysis (3,4)

Here's my advice: Work through each of the texts listed below. By "work through", I mean understand all proofs and do most of the exercises. This will bring her up to speed with roughly the average junior math major at the average US college. Note that prerequisites parenthesis.

1. Simmons, Precalculus Mathematics in a Nutshell
2. Axler, Precalculus: A Prelude to Calculus (1)
3. Stewart, Calculus: Early Transcendentals (2)
4. Velleman, How to Prove It: A Structured Approach (2)
5. Axler, Linear Algebra Done Right (4)
6. Niven, Elementary Number Theory (4)
7. Herstein, Abstract Algebra (4)
8. Apostol, Mathematical Analysis (3,4)