Tanking in zOMG is quite difficult, because of the way aggro has been proportioned. That is, certain styles grab aggro far faster than others, while other styles are unable to get aggro directed at themselves no matter how hard they try. Once you learn it though, it's simple.
The main problem with aggro in zOMG is healing. I don't have all the numbers handy, but trust me when I say that healers tend to draw the most aggro. To the point that its nearly impossible to avoid. There are some methods as to how to tank as a unique class, but they're pretty unusual, and generally less effective than other methods of combined tank-healer.
Your best bet is a healer tank. zOMG's abilities are fairly limited anyways, and this lets you double your usefulness by being both a damage-soaker and healer.
Solo: While it's difficult to be a solo healer/tank, you'll often end up in situations where you are grinding, repeatedly joining random crews, and thus will need a standard set as opposed to the time-consuming "have slots open" method that requires repeated null chamber visits. As essentials you need wish, bandage, meat, rock armor, and teflon spray. These basically make you able to soak decent damage, and heal your teammates until everything is attacking you. Mix and match fire-rain, hack, dervish, mantis, fitness, and healing halo based on what you're doing. More damage if solo, more buffs if you're grinding one boss lair with random crews. Divinity is also essential of course, but it's 100% safe to assume SOMEONE will have that, so not even worth mentioning.
Crew: In a crew you have time to plan, so no point in leaving anything up to chance. Your buffs will be predetermined, so take whichever are assigned to you. Most importantly you want Wish, Dianose, and Bandage. These three healing rings are huge aggro-getters, way better than taunt. You'll be saving your team and grabbing the attention of all enemies. "But wait, then I'm just a lame healer!!!!" Well, normally yes, but consider them zOMG's substitute for a good taunt. In addition, you want fire rain. It's great for aggro and steady damage over time, without knocking anything away from your team's melee like dervish does. Bring dervish and/or hack if your team can use a little extra damage, and doesn't mind knockback. Fitness is also pretty underrated. Check the stats screen for yourself, its pretty worthwhile. If you happen to own sweetheart, that's awesome too.
"But if I'm healing anyways, why not defib?"
Because defib is saying "I fully expect my team to fail." if you do it right, no one needs to die, and your ring slot is wasted
"What about diagnose? I heard its stupid and awful."
Diagnose is fairly bad based on its stamina cost, but it draws mad aggro. So use it at the start. Once you are tanking everything, you can ignore it.
"Turtle is THE tank ring, and you left it out!!!"
Turtle is awful. Seriously awful. its cooldown vs the damage it shields are just trash. It's better than nothing, but I would take it over almost any other ring. You can use bandage for better protection that turtle. It's just bad. Once upon a time, turtle was amazing. But its current stats just mean that you almost never want it.
Hope that helped.
You realise she asked for help with DMS specifically, right?