Final answer:
The brain stem structure most likely damaged in Maria's stroke, causing her to fall into a coma, is the reticular activating system (RAS), which regulates arousal and consciousness.
Step-by-step explanation:
If Maria suffered a stroke that resulted in her falling into a sleeplike coma from which she could not be awakened and we know that the damage occurred somewhere in the brain stem, the structure that is most likely to be damaged is the reticular activating system (RAS).
The RAS is a network of neurons located in the brain stem that play a crucial role in controlling arousal and the sleep-wake cycle. Damage to this area can disrupt its normal functioning, potentially leading to a comatose state where a patient cannot be awakened.