I suggest studying now and take the test in May or June, so that she can enjoy a summer without worrying about tests.
I think that a weekly 3-hour block of prep test is more effective than an hour here and there. The test prep service we used was for our son was a 10 three-hour course on Sunday nights, comprising of two 3-hour mock tests, the rest for mini tests and techniques, and with the last class meeting a few days prior to the actual test. All material in the course were printed, that is, nothing online, which I think is the key to success; the 3-hour format is useful for simulation of the real test conditions. Son did not study for the tests apart from the 3-hour course; he took the test in December of his junior year.