All iPads Can I email mp3 from Mac to iPad's iTunes

From my experience, I don't think you can add songs to iTunes on iPad -- you would have to sync it to your computer like an iPod or iPhone.

As for iCloud on PC -- yes, all you need to do is sign up with your apple ID or get one if you don't have it. iCloud is simply a server somewhere that stores data that we access remotely, so there's no need for 'putting it in a PC'. It works for all platforms, or at least I don't see why not. Now, I'm referring to the website itself where you can look at your data -- but if you want your computer to sync to your devises and vice-versa, then you would need a Mac, since it's built into the OS and its apps to interact with iCloud, and of course it's not on a PC, at least as far as I know of. That is, I'm not sure if Safari for windows would interact with iCloud the way it would on Mac OS X, maybe someone else knows?

But you should use iCloud -- it's great having your documents and photos, etc showing up on your devices!

iCloud doesn't work that way for music. There isn't a place you can just put music files on iCloud and they show up anywhere. Your mother would need to sign up for iTunes Match (24.99/yr) and then you would sign in to iTunes with the Apple ID she used to sign up for it.

Once signed up, any music you have in iTunes would then show up in her music app with the option of then downloading them to the device. It would be easier if you just signed her up for iTunes Match on your Windows machine. But keep in mind, anything you add to iTunes will be "sent" to her iPad.