Dell are fine until something goes wrong and I am sorry but I have heard more things going wrong then going right.
You pay for what you get with computers. Personally, I wouldnt touch any computer which runs a celeron processor, they spend more time falling over then standing up.
I have bought from PC World because I can at least go into the shop and have a face to face conversation with someone if it goes wrong. Unfortunately most of Dell's customer services are based abroad.
For a little bit more money - you can get a solid laptop which should give your mum plenty of years of happy surfing and some scope if she wishes to do more than just internet.