I would reject the ‘cis’ label for myself because i regard it as superfluous and pernicious. This is because it is a descriptor that comes from a belief system that many of us completely reject, because the beliefs revolve around sexist stereotypes that are harmful and are homophobic and specifically misogynistic. Anyone else can go ahead that’s their thing though.
I don’t think the below is a logical justification for using ‘cis’ as a prefix (if this was the reason?):
As my trans friend said to me, that she is always going to be a transwoman. Nothing is going to change that.
True, your friend can never become a woman. Nobody can become the opposite sex, everyone knows that. But if they are a ‘transwoman’ ie biologically male and transvestite or transsexual, then they already do not come into the category of woman. So it’s perfectly appropriate that they are not claiming to be a ‘woman’ or a ‘trans woman’ because that would be trying to be included into an inappropriate category group, women which by definition they’re not part of.
So to differentiate women from transsexuals or transvestites, no further embellishments are needed, because being included under ‘women’ is a category grouping that in reality can not be changed by what men do, and which should not be changed by what some men happen to want. So women can stick with the standard, factual category of woman.