Or you could make it yourself - if you have a printer...
Buy some nice A5 size paper that you think she would like, set the paper size in your word processor and play around until you get something that you like for the address.
Cut regular A4 in half (or to match paper size if different), print off a few test sheets to make sure the paper lines up and prints off as you expect it to, then print off the good paper. usually best to do it one by one or in small batches if it is not paper that is standard printer paper. Keep a few sheets plain as follow on sheets.
Buy a nice little plastic wallet to pop it all in, along with the matching envelopes.
Way cheaper than gettting it printed and you get double bonus points for having made it yourself. And if she likes it and wants more (or wants tweaks to the font or size etc) you can run off some more for her.
While you are at it you can also print off correspondence cards and add them to the set too.
Paperchase has some nice papers and envelopes that I think are suitable to put through printers and come in relatively small packs (eg 10 or 20 correspondence cards and envelopes, maybe 20-50 sheets of paper etc). I've done it in the past for my mum when she wanted some by buying a pad of basildon bond small paper from whsmith and tearing it off sheet by sheet 
You can even print up a sheet of regular paper with some thick lines on it like they had in the BB pads (no idea if they still do!) so you can write beautifully straight!
Places like whsmiths, staples and paperchase all have nice little plastic wallets which turn it from being a few little loose sheets of paper into a 'proper' homemade printed gift set IYSWIM.