The main thing is getting Deskyl's attention on her before she makes it out the door, which means DZ needs to be in the doorway, which leaves R4 on actual waking-her-up duty. It goes best if that's done with minimal startlement, and she has a system for what order to try things in to wake her as gently as possible.

Then R4 can do that!  ...from the side of the bed that's away from the door.  Y'know, just in case.

That's entirely reasonable of him!

The third thing he tries wakes the Sith, and she makes it fully out of bed and halfway to the door before noticing DZ and stopping short, tensed like a caged animal. DZ's signing calms her, though, and after a few minutes she gets her back into bed, leaving the doorway open for R4 to leave. (Deskyl notices him on his way out, and stares.)

R4 does not mind being stared at!  He only minds being lightsabered!  (Diana did, at least, cover his core processor in phrik, but it's not ever fun when someone tries to cut you in half!)

See you in eight hours?

    Yes, thank you.

It doesn't go as well the next morning; Deskyl has obviously forgotten most of what she'd gathered the previous day, and tries to order DZ out of the doorway rather than listen to her, her fear and increasing anger obvious in the Force as she does.

"...Let her, DZ.  It's not worth her being upset at you.  Sometimes you need to learn from experience."  Diana tries projecting peace-calm-we're-friends-here, for what it's worth, but is definitely expecting to need her lightsabers again.

Deskyl startles, visibly flinching, as she notices how close Diana has gotten, and falls back into a defensive stance, anger falling away into grim determination.

Diana just...stands there, for a moment, ready but not concerned, then goes to get Deskyl's food from the fridge.

This sends her from nihilistic determination to confusion and distress; when Diana gets back, DZ has her sitting on the edge of the bed and is trying without much success to get her to pay attention to a poem she's reciting for her.

Diana gives her the food?

Sure, that can happen.

Diana leaves her in peace to eat the food!  (An astromech occasionally trundles by.)

She eats; her emotions have settled out into vague despair by the time she's done. When she wakes again later, she's less upset, but the general tone is similar; DZ must know something to do about it, because it does lift a bit, back toward determination.

DZ waits for Diana to come out for lunch without waking Deskyl for it.

Diana looks over at DZ.  "...you know how I asked you to let me know if there was anything I could do to help?  I think you think I can do something to help your master, but I can't just guess what it is.  Or, I could, but I'd have anyone else's chances of succeeding, you know?  Jedi mostly aren't mind-readers.  Especially with droids for some reason that I am generally convinced is self-delusion; you think as much as I do.  So...what would help?"

"I don't have a specific idea of what to do, ma'am, but I do have an idea of what the problem is - I think Master Deskyl believes she's been captured, from her reactions."

"...Ah."

"...Could install a hard lock, give her the key?  ...not that it would help overmuch, but the problem is that she can hardly do keypads right now either..."

She also does have DZ's lunch ready.

"I wouldn't expect her to know how to operate a keypad or a hardware key, right now, ma'am. It might be best to just let her sleep? I expect her to have forgotten about it again in the morning."

"Mmm, true.  Still worth thinking about in case it's not different when she is awake and alert."  She hands off the food (and R4 is on standby to deliver it by now) and heads down to the cargo bay for practice.  "Til next time, DZ."

"...yes ma'am."

She'll try to talk to her again at dinnertime, then.

Diana does her katas for a bit, and then more ship-related stuff for the next few hours - tending the algae, etcetera.  Soon enough, she's back up on deck for dinner.

"Hello, ma'am. Did you want me to try any particular approach with Master Deskyl in the morning?"

"I don't know what you can do, DZ.  You're the, Sith protocol droid.  Tell me about the protocol, please."

...She looks...tired, all of a sudden, helmet off, face frazzled.  "I just don't want, to hurt her more.  There's already been so much pain..."  ...And she feels every wound.  "...Jedi, creatures of peace and life, fighting a war.  It's madness.  But so are the Sith, and the culture they espouse.  So who's more the fool?"

"...yes ma'am."

"Master Deskyl is a sensory specialist, and it's generally very obvious to her when there are other Force sensitives around; there are techniques that can hide you from her but my understanding is that they're difficult to hold for very long. If she can sense you, she'll be afraid of you, until she regains the ability to recognize you as an individual - I don't think that's avoidable; the understanding among Sith is that Jedi will kill them given any opportunity, and she seems to have retained that. But Sith are trained to handle fear, and I don't get the impression that it's necessarily distressing for her in this case; what she seemed to be distressed by today was the idea that there wasn't anything that she could do about you, which is something that Sith tend to be very sensitive to - I stopped her from attacking you, and you didn't seem to be afraid of her, and usually among Sith that would suggest that you'd already defeated her once and we were both confident that you could do it again - are you aware of Sith traditions around that situation, ma'am?"

"Nnnnooot in any particular detail."

"Yes ma'am," she nods. "Sith are very hierarchical; every Sith answers to a specific other Sith, all the way up to the Dark Council and the Emperor. These relationships can change by the master giving a Sith they have mastery of to another Sith, or by inheritance of a defeated Sith's assets - if Master Deskyl had managed to kill Lord Pritruth she would have inherited his property, his title, his direct allegiance to his Darth, and mastery of his other apprentices, assuming she was able to survive their attempts to kill her to inherit those things from her. Theft is another method, though not very relevant here. And directly defeating a Sith in combat also grants mastery of them, if you can do so without killing them - this is part of why Sith fight so viciously when cornered; it's the least stable kind of allegiance-change and is often worse than death, so they have no incentive to surrender. I believe this is what Master Deskyl thinks has happened to her right now."