Looks like the first thing you posted you just throw on top of your existing lens, I'm not sure about that one.

The Rokinon, I've read is a solid lens. Keep in mind that it is manual focus only (if that matters to you).

The 10-20 is indeed a wide angle - don't pay any attention to it saying "wide-angle" or not. Just look at the range for each lens (i.e. 10 is A LOT wider than 18).

To clarify, the multiplier for Canon is actually 1.6 (for the Canon 1DS series, it is 1.3), but from your Rebel to full frame it is 1.6.

I agree primes are sharper than zooms. It all depends on how your wife shoots. Is she going to want to be changing lens? Is she good with primes or prefer the convenience of zooms?

On my wife's camera we have a canon 15-85 efs. I would highly recommend it. I think it would be a good lens to try, as 15 is much wider than 18 and would give a good taste into wide-angle. (You can find them used from $400-500).

Now if you know for sure that you want to go ultra-wide the 10-20 mentioned or one of the other iterations (canons/ tokina, etc.) Would be a good way to go.