Since coming home that day I found out it seemed that everything was there to remind me about my thought of offering to be tested. Every time I saw a "Give Blood" advert on TV I would think about her and about offering to be tested.
I texted her a few times to ask how she was doing and even said to her "I'd give you my kidney if I could" to which she replied "Ah, that's kind of you, thanks" (I learnt later that this was a generic reply to all her friends who had said the same thing). Then I found out that she had been called up for a kidney and was in the hospital waiting to be called in to surgery when she was told that the kidney wasn't good enough to be used and she would have to go back on to the waiting list.
It was at this point (about 6 months after I first found out) that I texted her to ask her what the first steps would be for being tested as a donor. I don't think she realised how serious I was until I rang her to talk about it.
It took me a lot of thinking to actually take that first step. In the end I think it was time building up the courage to offer to go through some unknown experience that may have some unkown risks. I had read many websites and read forums galore and realised that in actuality the risk to a donor is a lot smaller than one might expect.