You cannot confront her the moment she lashes out, because then she's allready too exhausted to think about her behavior.
Inasead, talk to her in a calm moment like after a meal or when you are relaxing in the evening.
When talking to her, you must give her the following information in this order:
- What she does (how exactly she talks to you when she's stressed).
- How it makes you feel and how she hurts your feelings. Tell her that you'd gladly do the chores but her way of insulting you makes you not do it.
- What she should do instead or how she should talk to you instead.
The first step is to open the conversation and point out what exactly you're talking about. You both have to "be on the same wavelength" so you both talk about the same thing and understand the context. You can even think about recording her interactions with you and listen to the playback. This will probably make her understand exactly what you tell her next (how you feel about it).
It could also make her defensive or stressed. If that happens, she cannot think about her behavior and understand you. You must avoid blaming or attacking her in order to make her understand you. Make it about your feelings, less about her behavior.
The "I feel" approach does exactly that: You tell her how you perceive her actions and are affected by them. By doing that, you:
- don't attack or blame her ("you always insult me") but focus on you ("you hurt my feelings when you call me a pig").
- don't give her a chance to deny her behavior or accuse you of lying ("you always insult me" - "no, I don't")
- make it personal. It's not any stranger who's feeling bad, but her own child. People remember emotional experiences better than neutral experiences, so the chances of her remembering your conversation are higher.
- make her realize the consequences of her actions. She probably never thinks about how her words make you feel, because when she speaks them, she is too exhausted to feel empathy with you.
You give her the chance to reflect on her behavior and how it makes you feel without the need to defend against your words. As long as you stick to telling her how you feel, she cannot deny that you tell the truth. She cannot dismiss the conversation as a misunderstanding or overreaction to something.
The last point is important. It's not enough to tell her "don't do this". You should offer an alternative "do that instead". Tell her it's OK to be stressed and say so, but instead of insulting you, she could swear or punch a punching bag or something completely different. It's OK to "let off some steam", but instead of insulting you, she should do it in a different way. You can discuss this with her and find a solution together. This has the added benefit that she is more likely to accept a solution she proposed herself.
The reason why this is important is that she won't change her behavior over night. The next time she's exhausted, she'll forget your conversation and insult you again. In that moment, you can tell her
Please don't speak to me like that, do (alternative behavior) instead, like we agreed on.