We also know that Hillary Clinton, should she be elected POTUS, would never sign single payer into law either. Those are non-negotiable facts.
How do you refer to a potential future event as a non-negotiable fact?
Because there is no potential future event where she would do anything else.
First of all, she has many times taken a stance against single-payer. She is very clear on this, she does not support single payer.
Second, she is very heavily funded by wall street and insurance interests, who all oppose single payer. She would not dare take an action that would be so opposite their stands.
But even if she were to get hit in the head by a flying toilet and forget how she got there (assuming she ever were elected POTUS, which is far from certain), there is still the fact that there is almost no chance of single payer ever being presented to her as a bill. Look at the US senate election for 2016 (in spite of your consistent opposition to letting people vote in this themselves). There are 34 seats up for election in 2016, of which 10 are democrats. If the democrats completely swept the election (not a chance in hell), they would end up with 68 seats in the senate. The GOP would still be able to hold up bills like this as long as they want, and would still be able to terrorize democrats by calling them "Un-American" for proposing anything they don't agree with. Even then, the democrats would need to pull it off before the 2018 senate elections and they'd need to win enough of the house to make it happen. There is a better chance of you being named the next Tzar of Russia than those events happening.