You must understand that the English you does not correspond to the German Sie, but to du. So du is the normal form you normally use when talking to anyone you are familiar with: Family members, friends and colleagues.
The form of address »Sie« is known as honorifics which means »polite form« and expresses a distanced respect. Although you normally respect those close to you, this respect does not have to be expressed through language because these people know you and know from past actions that you respect them. But when you meet strangers, this shared past does not exist, so in many languages there are forms of politeness whose use signals that you honor and respect the other person. Old and Middle English had this form too (thou and ye for singular and plural) but it went lost in modern English.
The vast majority of people usually try to be nice and friendly to other people, and this includes respecting the person they are talking to. That's why German speakers usually use the »Sie« form when speaking to strangers.
If someone addresses an unknown adult stranger as »du«, there may be two reasons for this:
- rudeness and disrespect
- an attempt to appear close to the person being addressed.
What is meant by this must be inferred from the social context.
But the situation is very different, when you used to use »Sie« for a long time and suddenly switch to »du«.
If two people who are used to use »Sie« feel, that they have built up a friendly relationship through longer contact, then one person offers the other the »du« word. This is a relatively formal act, for which there is also a whole series of complicated rules, because you are leaving the realm of constant mutual expressions of respect, and therefore this transition from »Sie« to »du« involves a good deal of respect: Only the person with the highest social rank may offer the »du« (the boss may offer it to the employee, under no circumstances may the employee do so). If the two people feel they are of equal rank, it is up to the older person to make this offer, and if you are roughly the same age but of different gender, then it's the woman's turn to make this offer to a man.
Switching from »Sie« to »du« without this formal transition is always seen as an offensive act of expressing disrespect. Of course, this may happen unintentionally in a stressful situation, if this is the case, it is then necessary to apologize immediately.
But normally, even in a dispute, you remain respectful and do not switch from »Sie« to »du«. If you say »du« in a dispute with a person you would normally address as »Sie«, this is a strong act of disrespect and if you do this to a police officer, you can be punished for insulting the officer. (Newspaper articles: from 2020, from 2021 from 2023)
So the princess in your game can switch from "she" to "you" in an argument, but only if she is really very angry and if she really wants to end the previous respectful relationship for all time.
Something else puzzles me at your question:
It confuses me that the princess in your game uses the word »weasel«. I've never heard anyone say »weasel« to another person. This is not common in German and sounds funny and in such a situation even very irritating. A weasel is a very clever animal with an elegant body shape. It is agile and supple. These are all positive characteristics. Why would someone use this word in the context described? It doesn't make sense to me.