Sony Buyer

I personally prefer the Kindle 2.0 wireless reader, the International version. Some people prefer the Sony reader. For example, the Sony reader has back light functionality and a choice of ebook reader colours.

I would suggest you check read this blog for further info on the Kindle 2.0 and decide whether this is for you.

http://purchasekindle.info/kindle-2-0-vs-the-sony-reader

best of luck.
References :

I’ll suggest the Kindle, because it has free wireless and text-to-speech function. There are more ebooks you can find available for the Kindle too. There are some good comparison between them here:

http://www.amazon.com/gp/redirect.html?ie=UTF8&location=http%3A%2F%2Fwww.amazon.com%2Freview%2FR3ULAFVHBGYVQP%3Fie%3DUTF8%26ref%255F%3Dcm%255Fcr%255Frdp%255Fperm&tag=moreinfo-po-20&linkCode=ur2&camp=1789&creative=390957

http://www.speedreaderxreview.com/kindle-2-0-vs-sony-reader-prs-700bc-comparison

Hope it helps
References :
http://www.amazon.com/gp/redirect.html?ie=UTF8&location=http%3A%2F%2Fwww.amazon.com%2Fs%3Fie%3DUTF8%26rs%3D172282%26sort%3Dpmrank%26ref%255F%3Dsr%255Fst%26keywords%3Dsony%2520reader%26bbn%3D172282%26qid%3D1256199697%26rh%3Dn%253A172282%252Cn%253A%2521493964%252Ck%253Asony%2520reader%252Cp%255F4%253ASony%252Cp%255F36%253A10000-99999999%26page%3D1&tag=moreinfo-po-20&linkCode=ur2&camp=1789&creative=390957 (Sony Reader)
http://www.amazon.com/gp/product/B0015T963C?ie=UTF8&tag=moreinfo-po-20&linkCode=as2&camp=1789&creative=390957&creativeASIN=B0015T963C (Kindle 2 after price slash)

I’ll say the Kindle over Sony Reader. Read here to know more:

http://www.amazon.com/gp/redirect.html?ie=UTF8&location=http%3A%2F%2Fwww.amazon.com%2Freview%2FR266PE1Q47CYNH%3Fie%3DUTF8%26ASIN%3DB00154JDAI%26nodeID%3D%26ref%255F%3Dcm%255Fcr%255Fpr%255Fcmt&tag=more_info-20&linkCode=ur2&camp=1789&creative=390957

I own the Kindle 2 and I like it very much. It is better than Sony Reader because Amazon provide good content support, and the number of books available in Kindle format is kept on increasing (right now there are 300,000 Kindle books). Sony Reader, however, many users complain that it is difficult to find suitable books, and books on it are more expensive than the Kindle. Other benefits of the Kindle over Sony Reader include the free wireless internet access, and the text-to-speech function.

If your mama needs to read PDF with charts and graphics, you may want to go for the Kindle DX. Read this review and you should be able to decide which one to get:

http://www.amazon.com/gp/redirect.html?ie=UTF8&location=http%3A%2F%2Fwww.amazon.com%2Freview%2FR23V08M2LNB81I%3Fie%3DUTF8%26ASIN%3DB0015TCML0%26nodeID%3D%26ref%255F%3Dcm%255Fcr%255Fpr%255Fcmt&tag=more_info-20&linkCode=ur2&camp=1789&creative=390957

Hope this helps.
References :
http://www.amazon.com/gp/product/B0015TCML0?ie=UTF8&tag=more_info-20&linkCode=as2&camp=1789&creative=390957&creativeASIN=B0015TCML0 (Kindle DX)
http://www.amazon.com/gp/product/B00154JDAI?ie=UTF8&tag=more_info-20&linkCode=as2&camp=1789&creative=390957&creativeASIN=B00154JDAI (Kindle 2)