Dave, like Gajet, I too am a detectorist, you would be surprised how many of us are out there!
My suggestion too would be that she looks to join a local club where they can give advice. Some members might even have used machines they can loan/sell her to get her started. They will also have land and farm permissions at their disposal.
Try
www.symdc.co.ukThere’s no point spending a lot of money if it is just a passing whim. In my opinion it’s better to buy a good used machine than a bottom end new one. Avoid Maplins, their machines are toy-like.
It is luck of the draw to an extent as the item needs to be under your coil to be found. However, if you have a better machine it increases the chances of you finding the item once it is there.
Main dealers have new and used machines and will happily give advice, try:
www.joanallen.co.ukwww.crawfordsmd.comwww.regton.comGood luck!