If it all possible do an image back up of your mum's computer to an external HD before updating.
That way if things go wrong you can restore things back to the way they were before the update.
An image backup is an exact byte for byte image of your HD which is different then just backing up the data.
I backup my computer once a week to an external HD and have had to restore it a couple of times.
Once when I got a virus that pretty much fried the HD and one time when I installed a program that screwed up Windows.

I use a program called Image /for Windows, but there are other programs out there that will do the job.
One I can think of is called Ghost.

Good luck.

Tim