If she frequently experiences sleepiness or fatigue during the daytime, despite giving herself enough hours for sleep at night, then I would hope she would want to do something about that on her own. Listen to her and observe her, and eventually you will see a pattern of tiredness. You can then begin to gently coax her to see her doctor.
If nothing else, a lack of sound, true sleep seriously affects one's quality of life.
I know. I have Sleep Apnia, and have been managing it since 2003. The health risks are no joke.
One other thing to be wary of is if you notice her ceasing breathing while she's asleep. That is when Sleep Apnea becomes dangerous. It starves the brain of oxygen when it is supposed to be repairing itself. Over time this can lead to the more dire consequences you stated above.
Fortunately she has moved back into the MBR with you where you will have a better opportunity to listen to/observe her. So there's another good thing about her moving back -- if she does turn out to have Apnea, this move could potentially save her life.
You might be surprised how many people suffer from Sleep Apnea, including people you know, work with or socialize with. It's a lot more common than one would think.
