I think the issue here is not verifying if your stepdaughter is on-target with her public-schooled peers, but rather understanding both the homeschool philosophy and how children learn. In a classroom of 25 or 30 students, all of the children are required to learn the same thing at the same time. Out of necessity, individual learning styles, abilities, strengths, and weaknesses cannot be given careful consideration. Thus, all public-schooled first-graders are expected to grasp the fundamentals of reading, spelling, math, etc. Some do, many don't.

Homeschooled students do not have to follow this pattern. Parents can tune in to their child's abilities, and structure their teaching methods to accommodate that child's learning style. Thus, some kids begin to read and spell at four, while others may not be ready until they are nine, ten, or even older. There is no particular advantage in learning to read or write early, and there is evidence to suggest that doing so can be harmful. For more information about this, read How Children Learn by John Holt.

Most six- or seven-year-old children, including those in traditional schools, do not spell well. If your stepdaughter appears to be having a difficult time spelling, it may not be a problem with homeschooling, but rather that she simply does not yet have the ability to grasp spelling concepts. My daughters hated Scrabble when they were six or seven, but couldn't get enough of the game just a few years later when they matured a bit. I suggest reading good books with your stepdaughter as an alternative activity. Reading aloud is a wonderful way to develop children's language skills.

The Homeschooling Book of Answers by Linda Dobson will help you better understand the homeschooling philosophy.