Moving Photos from iPhone 7 to MacBook Air

I am trying to do something that should be rather simple, namely to move the photos on my sister's iPhone 7 to either her Windows computer or my MacBook Air. First, we connected the phone to my sister's Windows machine. We selected the photos to transfer and began to move them to the hard drive on her Windows machine. After just a minute or so of transferring, an error message popped up saying that the external device failed. Next, I tried to simply AirDrop the photos over to my MacBook Air. I selected 480 photos and and at first it appeared to be working. However, an error message popped up saying that the AirDrop failed. Next, I connected the iPhone to the MacBook using a cord and tried to transfer through the Photos app, but the app became stuck on "Preparing to import photos" or something to that effect. I am quickly running out of options to do something that should be rather easy. Please help.