So.. Druids Have one, Paladins have One....Follow

Druids and Paladins both have addons that tell you exactly what to use when.

I find it strange that Death Knights do not (or at least I didn't see one listed at Curse).

Situation: My mom plays WoW. She's 55 and she doesn't have a fast hand-to-eye coordination, and she has trouble seeing the itty-bitty little rune icons at the top of the screen and she seems to be a bit slow in understanding why I told her to use the buttons in the order I told her to.

That and I think she's not watching for misses on Icy Touch and Plague Strike, or she uses them too often (and doesn't have any runes for Obliterate (which I never put on her hotkey bar, to avoid confusing her) or Death Strike.

Basically, I told her to use "3, 4, 5, 5, ="

3: Icy Touch
4: Plague Strike
5: Heart Strike
=: Death Strike
6: Death Coil

And she does that for the most part. I know she SHOULD be using Death Coil, but she usually forgets. Blah.

Anyways, Paladins and Druids have this thing that pops up on the screen and tells you what you should use next... anything like that exist for DKs?

Alternatively, if it's an option for you, you can download PowerAuras. That addon allows you to set up specific graphics on the screen when... just about anything you want occurs. You could for example make a green glow appear over her target's portrait whenever a disease is(n't) up. It doesn't specifically keep track of runes, but you can technically vizualize your entire rotation in graphics with it.

Forte can be configured for any class. It's basically set up as a graphical bar that shows ability icons moving "down the bar" as their cooldowns time out and can be set to alert you when actions are available with minimum set up. Link here.

To pair with that I'd go with MagicRunes which can be set up any size and location as either icons or bars. Link here.

You could try this addon that someone suggested on the druid forum for a feral kitty. It works for most if not all classes/specs

Yes but I've kinda heavily customized my HUD. By default it shows your health bar, target health bar, then energy bars (energy, RP, mana, etc.). I enabled a bar for threat, created one for bone armor and diseases and moved where the runes are. You can reposition it or even hide different components if needed. The whole point of it is to give you information you want to know (you can even see my pet health/energy) in the middle of your screen so the focus is on the part of your screen where your character is. I love this, since it lets me avoid standing in void zones lol.

The problem with those addons that suggest what ability to use, is that its just a suggestion. If you try to do good dps by just following the addon, you will be handicapping yourself and your dps. I used to use feral by night and when I turned it off and actually learned the cat dps priority my dps went up by 5-8%.