Your toddler’s demands are more about behaviour than house rules, by this I mean while you are willing to negotiate their requests and explain again and again why these things are not possible or desirable she is motivated to discuss again and again and even to add more.
My suggestion is to explain once why not, then move on, if you become involved in a discussion, argument or trying to make their brain work on the logic that you are noticing them and it is worthwhile so they will continue, and believe me it doesn’t matter is you are discussing the in’s and out’s in a patient manner, a frustrated manner or a totally annoyed manner - to him/her and has involved you and you are discussing it with them so this is worthwhile and they will try the same topic or strategy again, again, and again.
By now, whatever the topic of negotiation is s/he knows what the rules are and what you require so avoid becoming unwittingly part of the process and stop negotiating. Or if appropriate just act without any words, sighs, looks etc. For example if you have indicated that the biscuit is not on, and she goes to the cupboard and gets the biscuit, the best way to manage this is to walk over and take the biscuit, no words, looks, sighs etc, she knows what she is doing is wrong and does not need to be told again, and actions will reap your more compliance than words. Take the biscuit and ignore or do not be drawn into the drama that she unfolds, if you do, you are making the whole scenario worthwhile to her and her brain will say, that worked for me, I’d better remember what I did and try that again tomorrow.
Also use this strategy to your advantage to mould and encourage the type of behaviours you value or desire, eg when she doesn’t ask for a biscuit before dinner, take note and say something like ‘ you have waited patiently for dinner’, she will also respond in the same manner by saying to herself, that was worthwhile, you noticed, and her brain will say, I’d better remember what I did and try that again tomorrow. Thus you are encouraging the behaviours you desire or value. This is the most powerful tool a parent has.