Yes, it is possible. But, as many others have said, it takes a lot of hard work and dedication from the student. My brother's girlfriend's family (8 kids, she's the oldest) for various unfortunate reasons were/are inadvertent unschoolers. The girlfriend (now late teens) decided when she was about 15 that she wanted to know more about maths. My siblings and I were homeschooled, and used Saxon maths. We offered her tutoring and the use of our textbooks. She started Saxon 54 in Feb, skipped to 65 after about 50 lessons, just over a year later she finished Algebra 1/2. She was doing up to 20 lessons and up to 6hrs tutoring each week. She worked very hard, and has reaped the benefits. (As an aside, she doesn't enjoy maths, and only learnt because her lack of maths skills was adversely affecting her life.) So, yes it is possible. She did have a general idea of addition and subtraction, but that was it. It has taken time, and while she probably won't ever go to university, she is now competent at maths and shouldn't have too many issues with it in life. If at all possible, help the girl learn, provide her with resources, and direct her towards possible learning avenues.