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> she acted nice with nice people
> she acted evil with evil people

It's called "mirroring" and it's a typical BPD trait. BPD girls have an unstable self-image. They tend to change their views and values to match the people around them in order to endear themselves to them and it's obviously a form of manipulation.

If you happen to meet a girl who claims to have a "sponge" personality, run.