Errm... iOS 8 turned an iPad _Air_ into a 'stuttering and crashing mess'? I've got a 32GB Air and haven't noticed any stuttering or crashing. I haven't noticed much of anything wrong with it, actually. Well, other than the fact that wireless backups don't work anymore, but that's not stuttering or crashing, that's just a straight out glaring bug which should never have got past QA.
I suspect that 'tis not iOS 8, but rather the combination of iOS 8 and some other software she might have installed. Which would be another straight-out glaring bug which should never have got past QA. Apple's QA has been going downhill for a while now. iOS 8 appears to be particularly annoying in that respect.