“She paid for the trip out of her own pocket.”

Your daughter's school club went on an overnight trip. You're concerned for the teacher, who paid for her own hotel room and food. You're talking with one of the other parents about it. You say:

She paid for the trip out of her own pocket.

pay for (something) out of (one's) own pocket

To pay for something "out of your own pocket" means to pay for it with your own money. 

People especially use this phrase when:

• they think that someone else should have paid instead (like in the example above, where the school should have paid for the teacher's trip)
• someone paid for something that was really expensive and hard to afford:

  No, I financed the entire company out of my own pocket.

You can only talk about someone paying out of their own pocket. It doesn't make sense to talk about one person paying out of another person's pocket.

Also notice that it's always "pocket", not "pockets".