What does it mean if a lawyer has affiliated offices around the world?

One lawyer I am interested in has 4 offices around the world. One office is near my area. What exactly does 'affiliated office' mean?

Does she seem like a good lawyer if she has these affiliated offices?

It means they have an agreement with those offices to do reciprocal work, if there is an agreement at all. How can you, as a client, prove this statement is true or false? I wouldn't know how to do that.