No No No No No No No

Couple of things that we tried and some worked at different times and her mood:

1. Make it a game when she goes nononono u go yayayaya with giggle and she laughs and forgets about no's.
2. Leave the subject for which no is about just switch gears.
3. make a song from nonono to hahaha hehehe etc suiting her age.
4. Whenever she is in yes mode show her encouragement and smile with no mostly ignore. Rewarding +ve behaviour. Suggest her to say I do not like rather than No... Its longer and keeps the no's saway...

Best of Luck!

Your insight that the behavior probably being more about her not feeling well indicates this might just be temporary.
Saying NO is one issue and whining is another. I made a habit of not responding to whiny requests to discourage the whining.
NO's can be frustrating & challenging but it was helpful for me to keep this in mind:
Saying NO is an important part of their development. If they are not allowed to express NO it will go underground manifesting in rebelliousness or passive aggressive behaviour. I also wanted to empower my children by allowing them to say NO to adults. This way they would be less likely to be taken advantage of by predators and bullies.

Ignore Ignore Ignore! How do you react when she does this? If you give a lot of attention to it, she might have learned that "hey my litany of 'no's really garners a response from mommy - I really know how to get her attention, so let's do it again!". We're in the 'if you don't let me assert my independence while in public, I'm going to throw a fit' stage with our kid, so when he does things like get angry because we want to put his milk in a straw/sippy cup so he won't spill it all over a restaurant...we let him melt down into his tantrum and ignore it completely. We draw ZERO attention to it, other than removing him from the environment and let him do his thing without an audience (supervised by mom, of course). We do not want him to learn that screaming/tantrum = getting his way, when we have made a decision that is in his best interest.

Obviously, make sure she isn't hurt or has some sort of immediate need that requires addressing.

Praise Praise Praise when she demonstrates appropriate verbal skills to express what she wants.

I agree totally with what the mom before me said. Ignore the bad behavior at home and do a time-out in public, so as not to disturb other people. My son went through that at about the same age as your daughter. What I decided to do was to tell him "no touch" for example if he reached for something that he shouldn't be touching. And then I showed him the things he was able to touch and telling him "touch" at the same time. Since then we have added other words to the "no", so we're not just saying "no" all the time but telling him what we don't want him to do, for example "no climb" or "no jump", etc. The key is to praise for good behavior as well. This is a really hard time becuase they are still learning to communicate and can't express themselves the way they want to. It will get better! Also, my son went through a phase where he would say "no" all the time, even when he meant "yes". For example, "Do you want some juice?" and he would say "no!" and then reach for the cup. Good luck!