se mettre en frais pour...

[KB Norton]

what does this expression mean?
For example, elle s'est mise en frais pour m'aider... etc.

[George Hunt]

I will guess that it means that she went out of her way to help me (literally she put herself into  expenses in order to help me).

Since "frais" means "expenses " that is my  guess.

I think the opposite might be to do someone a favour when it is no skin off your  nose.

[Yannick]

That's correct Georges. Se mettre en frais is To do something at one's own expense