There are many different lenses for cameras; Wide angle lenses, standard lenses, portrait lenses, telephoto lenses and more. Canon has its own brand of lenses but also Sigma y Tamron are offering compatible lenses for it, it just depends on the price and the quality you are looking for
Any Canon camera with the EF-S lens system will work. That includes but isn't limited to all of the rebels (XT, XtI, XS, XSI, and the new T1I). The only cameras that WON'T work with your Rebel XTI lenses are Canon 1Ds, Canon 1Ds Mark II, Canon 1Ds Mark III, Canon 5d, Canon 5D Mark II. Another other Canon digital camera will do the job. The reason that these won't work is because they are full-frame cameras, which need a larger surface area of the lens and will not accept the mount from the smaller EF-S lenses. These cameras are all professional cameras and cost a couple thousand each.
The Canon Rebel film bodies use the EF mount lenses. All modern Canon EOS cameras, including all digital EOS cameras will also accept EF mount lense. The EF and EF-S lenses are compatible with the Rebel series. However, the lenses that typically come with a Rebel (EF-S) are compatible only with Canon cameras that have a 1.6 crop factor. Cameras with the 1.3 or no crop feature will not accept the EF-S lenses. The lens mounts deeper than the mirror will tolerate.
If you're buying Canon lenses, you'll need the EF-Slenses for your 1100d.
Generally, no. Each manufacturer has proprietary mounts for their lenses and, for example, Nikon lenses will not fit a Canon and so on. There are aftermarket lenses made to fit various cameras, but you need to specify the make and even sometimes the model of the camera in order to get a mount that fits.
Yes. The lens' brand (Nikon for example) to your Canon adapter.
If you are interested in finding good, trusting reviews in regards to any Canon camera, there are numerous websites you can visit. However, the most popular and credible is Epinion.
Panasonic cameras are tricky in that they only accept replacement lens made by Panasonic themselves.
Hyperopic, plus powered, or convex lenses.
If you want great quality video then Canon is the way to go, while Nikon is also coming out with great video improvements, but it costs a lot. Sony on other hand has great cameras with excellent technology, but Sony cameras do not have a wide range of lens to choose from. It all depends on what you need.
Although often exposed to bright sunlight, not all outdoor security cameras have anti-glare lenses. Most do, however if you are thinking of purchasing one and will need this feature it is best to check the product description before you decide.
It depends on how old. Canon EF lenses made since 1987 for Canon EOS bodies will fit the new Canon EOS digital bodies. The older FD lenses (before 1987) will not fit Canon EOS bodies, film or digital.
It depends on what kind of pictures she wants to take, such as indoor or outdoor. Another important thing is her budget, they can range from a few hundred to a few thousand. I like most cameras in the Canon family with the PowerSD 4000 around $250, being a good budge start. To be more serious she will need something with removable lenses like a Cannon Rebel EOS T1i at $750.