Hell Richard and welcome to the forums.
I am not familiar with the two models that you have mentioned however I have just had a quick search of the web and found some information. For the £90 that you have found the Z10 there is no doubt that it is a feature packed and capable camera with some features that you would normally only find on much more expensive models. It can be used in full auto so that minimum amount of user input is required or if your girlfriend is more into photography (now or maybe in the future) the camera can be switched to various other modes or even full manual to allow her to be as creative as she pleases. This will allow her to grow into the camera and not feel too restricted by it. I also noticed that this model has a 8x optical zoom which for a camera of this price range is very, very good.
There is a plain english review/spec article on the Z10
here and an in depth review with sample images
here
The Z3 has a slightly higher specification with a larger MP sensor (4mp vs 3mp on the Z10) 10x optical zoom vs 8x on the Z10 and the other main difference is the inclusion of Minolta’s CCD-shift Anti-Shake System which will allow for steadier and sharper telephoto photographs. All this extra technology will cost extra money but you will have to decide for yourself if the cost difference will be worth it to your girlfriend.
If you are going to print out any photos from these cameras than you are looking at a maximum size of about 8” x 10” from the Z10 and very slightly larger from the Z3, although in reality modern software can greatly increase these options for you.
An in depth review of the Z3 with sample images is available
here
Hope that helps a little but I am sure that someone else will be along soon to offer you some more advice.
Edit I see Ct has beaten me to it again.