the big change coming this fall is the Merom CPU, which is essential Centrino 2 Duo, it will be 64 bit and quite a bit faster than the current Yonah (?) chips.
currently the only deal is a free nano if you use student discount (since you're a student, you qualify). Also Amazon (they sell the basic model with minimum everything) has pretty good sales once in while, upto $100 or so off Apple's price (granted its the base model, not good for everyone)
As in terms of what to get her, old people (i am not calling your mom's old, i am the same age as you, my parents roughly same age as yours then i figure) hate to learn new technology, it took almost a year for me to move my dad to Linux, my mom still doesn't get it beyond opening firefox and going on google. In either case, if she's a windows user, I'd actually suggest a PC, because it will be easier on her (i know boot camp blah blah blah, but if you're gonna run XP anyway, just get a PC). If she is familiar with macs, or is willing to go through a bit of a learning curve, then get a mac (not that it will be that hard to learn).
If by "trouble free" you mean in the hardware dept, then if you do go the PC route, ASUS is your brand (they used to build, maybe still do, apple's laptops), those things are rock solid. On the flip side, with an asus you cant go to your local apple store and bitch if you do have a problem....thats where macs rank supreme (the ability to go to the apple store and yell @ some1 if something is broken).
well either way, hope this helps.