I think it is a problem of not enough practice.
She obviously "knows" the concepts, since she could finish the tutor's sentence. Of course she has holes in her knowledge, need you to help her with missing steps -- this is normal, not a big concern. It is definitely not a memory problem, if she could remember the concepts, she could remember the numbers.
She probably did not do enough practice problems over the years, and now it's all showing up. The only way I can see is to drill with problems -- starting with mixed arithmetic operations, then to algebraic expression manipulation. Once getting over this hurdle, everything she learned will click together.
