How do you guys deal with a cranky wake up?

In the afternoon my grandma sleeps from 2:30 to 4. Since she doesn't sleep at night if she sleeps after 4 pm, we have been having her wake up at 4 (unwillingly) so that she sleeps really well at night. It's working but she is nasty when she wakes up. I mean she calls names, threatens our safety and holds a grudge towards me (mostly me since I'm the one on duty during this time) throughout the evening which is shocking considering she can't remember eating two minutes after she does so. Once 4:45, 5:00 or so happens she's wide awake but that hour before she's horrible and she says hurtful things.

Does anyone have any suggestions on gentle ways to wake up a person or a way to keep her awake? I'm just trying to get through the one hour time that seems to ruin most of the evening. I'm not sure she remembers her yelling and threatening afterwards or just remembers the feeling in her stomach of having yelled towards someone. Either way she refuses to eat, refuses to talk and sulks for hours afterwards making dinner very difficult. I'm not sure how much she remembers but I'm not sure how to handle it. I mean all day and night she's fine. She's pleasant, nice and generally fun to be around. It's just this one hour and it really makes a difference. She is sleeping amazingly at night to the point of where my mom is having to wake her up after 3 to 4 hours for fear she will have an accident. We were frustrated and tried to let her sleep in the evening for a few days to avoid waking her up and dealing with the mood swing and we had miserable nights where it would continue into the days. She was upset all day, yelling all day, complaining so this waking up at 4 really does make the difference between a good day and a bad day.

Any suggestions anyone might have or even the admittance that we aren't alone (which we might very well be) would be helpful. I'm just at my wits end as to what to do at this point with that one hour time frame...