Lots of responses, thankyou.
To put a bit more meat on the bones, the situation is, as some have pointed out, awkward.
I am battling my need and desire to generate both portfolio examples and exposure to wider clients vs profit. At the moment, as my photography is a hobby really and I only make a little money here and there, I don't need the money as such but I am also concious that I do not want to cheapen my own work or that of the industry - digi shooters are doing that for us!
This situation arose by their desire to have some nice pictures and they asked if I'd do it. If I hadn't had agreed, they'd have used some other commercial bozzo who'd do it for £50, and then he would not doubt get all the resulting word-of-mouth recommendations instead of me. And they are my best friends, but I have now learnt this was not such a good idea.
Suffice to say that I explained everything we have said and likened it to buying an Aston Martin but then servicing it yourself using oil and spark plugs from Costco. She is 100% certain she wishes to buy 4 enlargements for her wall, which she understands need to be done from the negs. In fact, she's sent me the numbers already. So that's good. The onyl reason she wanted the proofs was for her to make her own little album to look throwugh now and again - no doubt it will seldom see the light of day, unlike the wall prints.
So, all in all, not a bad resolve. Yes, she has the proofs and yes she will be printing them herself - hopefully if kept 6"x4" they won't look too horrid. But, if our friendship has stayed in tact and she has ordered some top notch versions for her walls, that will be seen by every visitor to her home, then on balance, I think its worked out OK.
A lesson learned. I won't be doing it again I don't think and if I do, I'll treat it more formally, with a contract etc.
Thanks for the advice guys.