A cloud solution is the easiest way yes.
One of the easiest ways is to use the Photos app on your Mac. It can automatically upload yours images to iCloud. You can then install the iCloud for Windows app (assuming her work permits this). Any new pictures, edits etc will be synced. This also has the benefit of automatically uploading and photo you take on iOS devices too.
You could opt for another cloud provider, Google Drive/Photos, One Drive, Dropbox, Box etc, etc.
These offer a similar service; you install a client app on OSX and Windows. The difference with these is that you typically have to save your pictures to a specific folder on your MAc but then they sync automatically just like the iCloud solution.