Hi J.,
This is a perfect opportunity for you to teach your child about boundaries, respect, obedience, delayed gratification, lots of things. She's two, so she's certainly old enough to learn these life lessons. I nursed my son until he was two, and wish he had been eager to continue.
Both the "fight for nursing" or the "constant stopping and nursing" are unacceptable -- you must now draw some clear boundary lines for your daughter that do not include catering to her every whim. Remember, before she is one, her wants and needs are the same, and there is no such thing as spoiling her, but now that she's two, setting limits is not only appropriate, it is necessary, and she needs you to do it to make her feel safe and secure. A child without such boundaries ends up feeling very unhappy.
I would suggest you sit her down and tell her that she must ask you before she may nurse, and that she must do it a certain way -- putting her hand on your arm, waiting for you to acknowledge her (put your hand on hers) and then asking you respectfully. If you are in public, she must whisper her request in your ear (not, "Mama, I want to nurse!" in the middle of the grocery store...!) Tell her that if the answer is "no," she must not whine or fuss or ask you again.
Set her up -- take her somewhere she loves, or, if you have to shop, start loading things into the cart that she loves, and if she whines or asks you again, abruptly drop everything (those fruit rollups and juice boxes -- make sure she sees you dumping them) and LEAVE. Let her know that her choice was not a good one, but you're sure she will make a better choice tomorrow.
You have to train her to obey, to follow your rules, especially when you've established new ones. That means set up lots of situations in which you two can "practice." It sounds like you need to practice being more consistent with "No means No."
At night, after you have nursed for the last time, if she asks again, you can tell her "nurse went night-night." My daughter was desolate to hear those words, but tenderly kissed my bosoms and said, sadly, "Night-night, nurse, night-night...." At least I had put it in terms she could understand....
The bottom line is you have to pick a way of doing it and stick to it without exception (unless you are comfort nursing like when she falls down or something) -- ie., "we only nurse at home," or "we nurse before breakfast, lunch, dinner and night-night," or "you must ask me nicely to nurse, or the answer is 'no'." Find what works for you, and then be absolutely consistent.
There is nothing wrong with lots of nursing at the age of two, but if you feel it's time to slow it down, or if catering to her nursing whims is wearing you out, then it's right to set clear parameters. What is going on here is your daughter has found a way to control her environment, and to feel powerful. Make her feel powerful by seeing the results of her good choices, her polite and respectful behavior. The rewards for those should be wonderful. And the consequences for whining, tantruming, insisting, repeating her demands (shows disrespect for your "no") etc. should be swift and consistent. This means you'll have a few days of complete hell in which you will feel exhausted, after which, bliss! peace! relief! harmony!
All the best,
S.