HiTudor Bell and welcome from me,too.
Well done for taking on this hen, she certainly sounds in need of care. As you say that she is friendly and seems to be someone's pet, have you been able to put up posters locally about her? It's quite possible her owner is having sleepless nights worrying what has happened to her and whether a fox has killed her. We had a similar case on here recently, where someone took in a stray hen, looked after her temporarily, and then succeeded in finding her grateful owner.
I wondered if you had found the link to the main Poultrykeeper website, see the bottom of the page, also here http://poultrykeeper.com/ which has lots of helpful info on keeping chickens, in case you haven't had any before.
As Chris says, her main needs will be a secure coop and run, and also she will need to eat layers pellets, which you can get at any agricultural store, and also at Pets at Home if this is nearer to you. She will need a supply of grit and oystershell, in a pot to pick at when she needs it, and of course clean fresh water. If you can't find her owner and do decide to keep her, you might like to buy a proper poultry feeder and drinker as these will reduce spillage and contamination when she scratches. Check her over carefully to see if she has any parasites. Look under her tail around her vent, and under her wings and round her neck, checking for small white eggs or dirty- looking feathers. She may also need worming.
Don't worry about eating the eggs, if she appears bright and healthy I think they're just her little present to you as a way of saying thank you!