These are all entry-level
DSLRs.
My mum has been using 550D/T2i for around a year with the kit lens. Her prior experience (as well as mine) in photography was limited to digital compacts and so far she is happy with how much the camera empowers her to try skills of a slightly higher level.
The kit lens that come with the set is a good starter lens. Focus is fast with image stabilization. Unless you are into
pixel peeping, image quality is also quite acceptable especially at the centre area.
Bokeh (blurred background) is okay as long as you use the telephoto end of the lens with a wide aperture. On top of that its light weight (200g) makes it a good companion to the more portable entry-level DSLRs.
The main problem of the lens is the resulting images being a bit soft at the borders, and the lack of a "punch" due to the less-than-vibrant colours.
Chromatic aberration and
vignetting are pronounced at the mid-length and the wide-angle end respectively, though these are not problems exclusive to starter lens. Nonetheless cost-performance is excellent - you simply can't find anything better at the $100 price range (except maybe the 50mm prime for the impeccable sharpness but the fixed length is limiting in itself). But to bring out the full potential of the 550D/600D sensors better lens are necessary.
The camera itself is of solid quality. Weighting only 530g it is quite portable when compared to other more professional models. The APS-C sensor is also decent enough offering an acceptable ISO capability in low night conditions, usable up to ISO 800 (noise starts to become glaring from ISO 1600 and onwards). For image quality alone it is true that you cannot compare it with professional models like 5D Mark II, but with good lens it is at least as good as 7D which is around 2-3 times more expensive.
Ergonomics is fine for Asians but less so for Europeans/Americans. The camera fits comfortably in my mum's palm and she can hold it in one hand. But if your mum have hands larger than the Asian average, an additional grip may be necessary. It may be a good idea to try it out first in a shop.
We seldom if ever shoot video so no comment on this regard, but Canon cameras are known for doing a good job in this area.
600D/T3i is an upgrade of 550D with the addition of a swivel-and-tilt and a number of beginner-friendly features. The core specifications as well as the sensor are essentially the same as 550D however. Whether this limited range of new features justifies the $200 premium and an additional 40g is an issue of personal preference.
1100D/T3 is a budget model in the starter-DSLR line with a weaker sensor and a worse display. With a weight of 495g it is however marginally more portable than 550D/600D, but the difference is not that significant. If you hate dragging a brick around, the negligible weight advantage may be slightly relevant.
Do remember that the best camera is not the one with the highest quality, but the one that is always with you - a major reason why I am still using a digital compact instead of stealing the 550D from my mum.
Btw Nikon also offers decent entry-level DSLRs and you may also be interested in looking into those. I have no experience with Nikon though so you may need to find someone else for advice.
550D/600D:
Sensor: 18MP
Exposure Compensation = -5EV to +5EV
Video: Up to 1080P
Burst: 3.7 shots / second
LCD screen: 3 inches, 1.04 MP
1100D:
Sensor: 12MP
Exposure Compensation = -2EV to +2EV
Video: Up to 720P
Burst: 3.0 / second
LCD screen: 2.7 inches, 0.23 MP