Mice and keyboards are extensions of our own hands. We can tell you how nice a mouse feels in our hands but that does not mean it will feel nice in hers. We can also tell you about the quality and robustness of a mouse but if it does not feel good to her, then the point is moot.
Is she right or left handed? Does she have large man-hands or dainty child-size hands? Does she like a large or small mouse? These are things you cannot (or should not) decide for her.
Some people like a contoured mouse, others hate them. I don't like them. Even though I am right handed, I used my mouse with my left hand but I keep the buttons configured as a right handed mouse (I did this RSS pain years ago and discovered I was more productive this way since my number keypad is on the right, I can more easily work the keys and the mouse at the same time. But that's me. Most contoured mice are set for right-handed people.
You need to take her to lunch and then visit BestBuy or OfficeMax and let her play touchy-feely with the mice on display to see what feels good to her.
FTR, I use the
Wireless Comfort Desktop 5000 Combo Set. I don't know who makes the keyboards or mice for Microsoft, but both the mouse and keyboard have a great "feel" with a nice positive key-click. And the curved layout and wristpad means no RSS pain for me. The mouse is uni-shaped for either left or right and for me, and I guess you could say it is medium size. I have dropped the mouse onto the hardwood floor and except for the battery compartment cover flying off, the mouse keeps working flawlessly.
The mouse also has what MS calls BlueTrack Technology. This uses an optical laser system that works on almost any surface so no need for a mouse pad.
Because the keyboard and mouse are a set, it uses just one USB wireless dongle and that is nice and convenient. Being wireless, you do have to replace the batteries. I am on my computer about 4 - 6 hours per day and I have to replace the batteries about every 6 months. No big deal. And I do recommend wireless. Much more convenient IMO.
I see you are in the UK. Misco has the set for £48.95 Ex VAT. They do sell the mouse separately but then if she gets a wireless keyboard at a later date, you may end up with two wireless USB dongles and that can be a PITA.
One thing I have noticed over the years is when you buy a cheap mouse - it really feels cheap in your hand.