Be careful about weight, the new SL1 weighs so little that with a super zoom it might be too front heavy and she might not like it. Maybe you'll have to sacrifice a little bit of reach and get something like the Sigma 17-70mm f2.8-4 OS (the new version weighs about 100grams less).
Unless someone releases a battery grip for the SL1, most zoom lenses will feel front heavy with this camera... which might annoy some consumers who just want small, light, and nice handling.
As for which super zoom, the Tamron 18-270 VC seems to be the best of the bunch.
EDIT: The 18-270 VC weighs almost the same as the Sigma 17-70, it is also the lightest super zoom.