Final answer:
Maria should take her lithium two days before the visit, on Tuesday.
Step-by-step explanation:
Maria needs to take her lithium at a specific time on the day before your visit. To determine this time, you need to count two days back from the scheduled visit. If your visit is on Thursday at 8 AM, two days before that would be Tuesday. You should call Maria on Tuesday and ask her to take her lithium at that time.