For text books the main consideration will be availability in a usable format. In addition to the formatting, availability and cost of the needed texts in general may be an issue. If the book if formatted properly for an e reader, there should be no problem with images etc displaying.
There book apps such as Calibre (free software) which provide readers for PC and laptop; if she has to carry a laptop anyway this may be the way to go. Otherwise, she'd be carrying two devices if she needs a computer and then a reading device.
The biggest consideration on devices is whether you want a dedicated reade which provides a more pure ( more paper -like) and less eye strain reading experience ( Nook etc) or a reading app on a tablet which works just fine except for screen issues such as glare and eye strain.
When I get to my PC I will post some links that I used to help me select my e readers: we have two Nooks. I've also done a lot of reading on my iPad with the apps, so I've gone both ways.