If she is trying to be American, she is doing it poorly. I'll explain our system below and would love it if somebody could reciprocate for the UK.
Here it goes like this:
Ages 2-5 - Depending on many factors you might send your child to a "Mother's morning out" or "preschool" program at a local church. These would be private options. Some cities are also offering "head start" programs in lower income areas for these kids so that they at least have some classroom experience. If you are sending your child to a religious based school for their entire education they may have K3 and K4 programs, which is generally equivalent to a good church based program.
Age 5-6 - Kindergarten - Considered the final year by many of preschool. Kindergarten graduation is a common thing. However, in a very large school that might be K3-12, it is part of the elementary school. Kindergarten isn't required by most states. Kids can literally do no education at all until they are six or seven and yes, that does happen.
Ages 6-11 - Elementary school - typically grades 1-5, but in some areas 1-6, K-5, or K-6. It can also be called primary school or at a fancy school it might be called lower school. There are no tests or anything you have to take to go to the next level. The states always have some sort of pointless standardized tests.
Ages 11-14 - Middle school - also sometimes called secondary school, junior high, intermediate school, or at a fancy school it is the point you move the upper school. It is typically grades 6-8, but if the elementary program encompasses grades 1-6, then the middle school would be grades 7-9.
Ages 14-18 - High School, sometimes upper school, generally grades 9-12, but sometimes 10-12. There is a state graduation exam everyone must pass to graduate. Kids also take the ACT's and SAT's for the purposes of college admissions.