Can you use iPhones in Jordan?

Only if its unlocked for use with all carriers, and Jordan carriers support similar enough cellular bands to the U.S.: https://www.apple.com/iphone/LTE/

Also note that warranty will only be valid in the U.S. and would need to be returned to the U.S. for any service repairs.

You don't "do the unlock", you buy an unlocked phone directly from Apple.

Only the carrier a phone is locked to can authorize unlocking it. Apple is the ONLY source for unlocked phones in the US at retail.

You need to buy an iPhone from Apple, and specifically ask for an unlocked model. Buying from places like Best Buy, or Target will not work. Those places do not sell unlocked devices. It must be purchased directly from Apple, and an unlocked model. Buying a model for AT&T or Verizon may not work either.

Then if she already has a service line in Jordan, she can use that or go to a carrier and request a sim card with service from them. Yes.

Again, there is no guarantee all bands are compatible, and no guarantee, a Jordan carrier can support an iPhone. And again, Warranty will only be valid in the U.S.