Also- know that if you are sick, you can pass certain illnesses on to your bird...Strep, for instance and certain types of bacteria. Whenever you are sick, it is very important to wash hands and not allow your bird up in your face etc, and never let a bird eat off of your plate/fork after you have eaten from it, as germs in our saliva (even if we feel healthy) can technically make them sick in some circumstances. Similarly, kissing on the lips etc should be avoided. Lots if people do these things, but it's really unwise.
On a related note, the saliva of cats and dogs =particularly harmful to bird----especially cats. A cat bite or cat scratch can kill a bird from infection more easily than the bite/wound itself (which is why even the smallest injury from a cat to a bird needs to be addressed immediately, even if the wound is very minor).
If anyone in your home has respiratory sensitivities or asthma, a powder-down bird (including cockatiels) should be avoided. Bird dander can be a real irritant, and the powder-down varieties produce a dust that is essential to their health, but often upsetting to sensitive human lungs.
They are ALL very expensive and very very very messy. The larger the bird, the higher the cost and mess, but even the small ones can put a serious dent in your once-clean home and wallet lol. They will poop on things, so consider how your mom will respond to that and how you want to prevent damage, as keeping the bird locked up isn't an acceptable means of mess-containment.
Another thing to be mindful of is that you will not be able to paint or spray for bugs or do many home-improvement projects in a rental once you have a bird (no glues, stains, paints, polishes, carpet shampoos, insecticides, scented products, standard household cleaners etc). Cleaning with standard household cleaners will be totally out of the question, so if your mom is really into Lysol, Bleach, Windex, ammonia, soft-scrub, Scrubbing Bubbles, air fresheners, and other common disinfectants (the list goes on), you will want to convince her of a bird-safe alternative ahead of time, because their respiratory systems are way more delicate and specialized than that of mammals'. F10 SC is a very safe avian veterinary disinfectant that kills a wide spectrum of viruses and bacteria (can be used to sterilize surgical equipment at the proper concentration), so from one germ-o-phobe to another, she might appreciate it more than something more "natural" that won't kill certain nasties. FYI- if you look into F10, the yellowish clear kind is no-rinse, but it is a concentrate, so you get a lot more bang for your buck than you would think for such a small bottle (I do 2ml to 17oz water and that ratio is pretty good at killing most stuff and it makes GALLONS---plus, it's good for 6 months after you mix it with water, unlike many other cleaners whose efficacy degrades within 24-48 hours of mixing w/water- you just will need a chemically resistant spray bottle to store the mix in and you can get one with ounces already marked on it at Wal-mart for a few bucks)...Oh- and the green variety of F10 is soapy, so it has to be rinsed off (it is also a concentrate), which is why I do not like it, because I do not rinse my home when cleaning indoors lol (you can use it if you prefer, but rinsing is required). If you use the yellow/clear kind that I use, you will want to figure out a way to stay on top of crusted on poop though, because the no-rinse f10 is just a disinfectant, not a surfactant, so it won't break down grime any better than water would. You have to remove debris before using it to clean. Toothbrushes can be useful, as can baking soda and certain scrubbers, as long as you never mix chemicals and pay careful attention to not destroying the powder-coating that you may have on your cage. In case it was not clear, I use F10 in my house/counters/toilets etc, as well as on the bird's cage.
Also- no candles, scented oils, aerosols, Glade Plug-ins, wax warmers etc...and no air fresheners in your home or car. Fabreeze has also been linked to bird deaths.