Did you read Anemone's logs as A2 while in the Resistance Camp? They gave A2 and Anemone's backstories, which explain A2's sentiment towards YoRHa.
Essentially, A2 was a prototype YoRHa unit sent on a mission to Earth. Her and her squad ended up joining forces with Anemone's squad. After being attacked by machine lifeforms and having units suffer from logic virus infections, A2 was forced to mercy-kill her own companions. Later, when it came down to it, she was not sent reinforcements and was left for dead. She managed to survive, but deserted afterwards, living on with the knowledge that Command betrayed her. On top of this, having deserted YoRHa, she is now hunted by YoRHa E-type units.
To her, the goal of the mission was to destroy the fusion reactor. In reality, the goal was to collect combat data for future android models. I think A2 was able to put two and two together and realize that she was being used.
So, not only was A2 deserted and betrayed, she is now hunted by the organization that she was once a part of.
In terms of what she is implying-- I believe she is accused of betraying YoRHa by Command at that moment. This is her rebuttal to that. It makes sense if you take it at face value, but there is added meaning, given the fact that
2B is based on the original A-class unit, which is what A2 is. In some sense, 2B is simply a newer A2. Anemone even hints at the similarity when she nearly mistakes 2B for A2 upon meeting her.
I was able to find a general summary of what happened during the Pearl Harbor Descent here. This should give a general idea of what happened and why A2 (correctly) felt betrayed.