Once you have the ISO in bootable format on the USB drive it doesn't really matter what happens to the original source it came from. you can do whatever you want with it.
The ISO by itself is not bootable you need to extract it from the iso format and leave all those files in the root directory of the drive in order to be bootable
so you would have extract the ISO to the SSD with something like Rufus, then boot to it on your friends computer but the SSD will not be available for installation you need another drive for the windows installation
if your wondering if you can install windows from an iso without a USB drive you still can but it will be a windows upgrade not a fresh install and you will have no control over formatting drives or changing where windows is installed.