If your daughter takes her junior year off before starting AP Spanish as a senior, it will have no negative impact on her college verdicts whatsoever. The admission folks will focus on the fact that she chose the highest level of Spanish available to her at her high school and not on the fact that she took no language at all in 11th grade.
Thus “The Dean’s” only concern is that your daughter is ready for the potential rigors of an AP class after studying Spanish online as a sophomore and then taking no Spanish as a junior. When school starts in the fall, it would be wise for her to meet with the AP Spanish teacher that she will likely have the next year (or with the head of her high school’s Spanish department) to get an overview of the AP curriculum, to confirm that she’s covered the necessary prerequisite materials, and to ask for suggestions on how to keep her language skills –both spoken and written–fresh during the hiatus.
If she is considering taking an SAT Subject Test in Spanish, she should try a practice test at home (available through books or online) to get a sense of where she stands before committing to the real deal.