TamiHi,
I exactly had the same problem a year ago. My SWCAH daughter, who was very good in nursing at the beginning, just started to prefer the bottle after a few months. I pumped the milk for 5 month, which I really hated, because it is time consuminig. So finally I stoped giving her breast milk when she was 8 months.
If I had another child, I would do everything to maintain nursing to protect her immune system. I am convinced that it is very important. Just like Sandra, - after consulting with our endo - we also stopped giving her the extra salt (she received one miligram of salt) when she was about 6 month-old, and it did not cause any problems.
At the beginning we gave her the salt in 200ml (~8fl) milk, but later on I decided to use natrium rich mineral water for the milk.
I am not a lactation consultant, but I know, that many reasons might behind the refusal of nursing (e.g.: it might consfusing for the child to nurse and eat from the bottle - because different techniques are required). So, I am sure that she will be able to give some good advice.
Good luck,
Tami