I agree with the recommendations for a Dell package, especially if it is for someone who is not very computer literate and a geographic distance from you.
Dell's customer service and support is second to none and will make YOUR life less stressful when trying to provide computer support for your mother.
As far as accessories go, I recommend one of the all-in-one packages of printer, scanner, fax. Rather then having 3 pieces of hardware for your mother to master, she'll only need to master 1 and then learn how to use the software for each application.
This one in particular is an incredible price and should meet the needs of your mother for several years... The free shipping program ends today so if you want to save on that, you'll need to make a quick decision.
http://www.dell.com/us/en/dhs/offers/specials_3x_special61.htm
If your mother has no need for a scanner/fax combo, then Dell has a printer deal you can add for an additional $200.