How likely is it that a 58 yr old female may have alzheimer's? I'm her daughter&i got results of genetic testing saying that I do have gene mutations.

No answer. It is not practical to answer your question. You should consult a neurologist for proper evaluation.
Alzheimers. Not everyone with the gene deveops the disease and the gene can stay suppressed by being mentally and physically active. That being said this is a discussion for your and your doctor.