Your parent will need to be logged in as herself, not you, to reassign a test.
To do so: Go to the OPTIONS FOR STUDENT tab and choose ASSIGN TESTS, then choose the one(s) you want and push the ASSIGN TEST option. It will not cost you if the test has previously been assigned to you.
Then you will need to log on as a student to be able to see and retake the tests.
I hope that helps.