Actually, I disagree with this in practice.
I do agree that you should be able to say how you feel, but "You fucking changed my CSS" is an overreaction. I work on a project with 4 or 5 other people. Sometimes they change something and it breaks me, and sometimes I change things and it breaks them. When that happens I can choose to react in a few ways:
1) "You fucking broke my code."
2) "Why did you change my code?"
3) "Why you change THE code/Why did you make this change?"
4) Ignore it and fix it myself.
Of the 4, #3 is probably the most appropriate reaction and can easily be stated as "Why did you make this change? It broke functionality/function X!" And it easily conveys the issue and your dissatisfaction.
She could have stated, "Why did you change my copy? I carefully selected each word and I think the changes detract from the overall feel." Boom. Done. Dissatisfaction has been conveyed without sounding like a child.