Ok, so the main thing I see wrong here is that she's running deffkoptas in the beginnings of a dredmob. she has a horde army, which tends to move pretty slow. Deffkoptas are very fast, leaving them exposed and easily killed if you fly them ahead to get behind the enemy lines. Since they have no support, they'll drop like flies. If you choose to run them, I'd strongly recommend getting a few boxes of Lootas and running at least 10-20. That way, the shooting can take some of the heat off the Deffkoptas before more help arrives. Also, you can drop the koptas altogether and instead get more Kans or boyz.
If you run a horde army, I really strongly recommend getting 2 big mekks with KFF's. That 5+ cover save is invaluable to keeping the orks alive longer. Another thing about the KFF, if you put your Kans and deff dreds within reach of it, they count as obscured, and since they're so big, put your little boyz behind the walkers and then your Orks will have a 4+ directional cover to all fire from the front.
If you want to get started on Orks, I'd recommend trying to run a speed freakz army as the foil to your fiance's. Speed freakz don't have the same number of boyz as a dredmob or straight up horde, but they're highly mobile and can be pretty surgical if you want them to be. Something to keep in mind about running transport spam for orks though, their AV on tanks is not too much different from wet cardboard, but there is a way to keep them more protected without wasting points on a bunch of useless upgrades: KFF. Stick a Big Mekk in a trukk or a Battlewagon and his 6" cover bubble extends from the hull of the transport, granting the vehicle he's in and all vehicles around him a 4+ obscurement. This is particularly powerful if you can keep your opponents shooting at the front of a battlewagon. 14 AV that always has a 4+ cover? Part of the amazingness that is Orks. Speed Freakz run a lot of transports (Trukks and Battlewagons), bikerz, and deffkoptas, anything that moves fast.
The ultimate idea behind orks is to not strike in waves. Hit hard with everything all at once and overwhelm your opponents. If it's a horde, you make up for speed with numbers. If it's speed freakz, you make up numbers with speed and precision.
If you're fighting dark eldar, they're kind of a tough match up for orks. The Dark Eldar's speed is only rivaled by the eldar, but the key thing about dark eldar is that their tank's armor is just as bad as Ork's are. Get a bunch of lootas and blast their fragile ships out of the sky with d3 S7 shots a turn, then overwhelm them with the number of orks you have on the table. As for Space Puppies, make sure they don't the charge off on you first. The best way to do this is to stick your scary, yet completely disposable killa kans in front of your boyz. They pack a hell of a wallop if the enemy leaves them alone, but they're so cheap that a squad of SW's taken out will make up their points lost.