Ok this may appear complicated at first but it could be done somewhat easily if setup correctly to begin with.
It requires one app on the iPad and one "app" on your machine.
Use Dropbox desktop client to create a MAIN FOLDER in the cloud
-- this is where you will put your subfolders and all your pics etc.
One your moms Ipad, download and install goodreader app.
In goodreader YOU (not mom), will setup and automatic sync option to sync with the MAIN Dropbox folder you created. This must be done once to initiate the sync information and store it for future use....
With the automatic sync setup you will also tell goodreader where you want the "items" to be stored locally on the goodreader folder structure.
Then you can start uploading content to your MAIN folder and then all MOM will need to do on ipad is open the goodreader app and find the sync button... then press the sync button in good reader to sync with the folder you told it to and it will pull everything in the folder down to her ipad and place it into a folder/directory that you determine.
She can then view the photos in a slideshow or whatever the case maybe from WITHIN goodreader.
Unfortunately there is no way to do this with the standard photos app. She will however have all the files downloaded on her system and won't need to be online once it is complete.
See the following for the detailed instructions.
http://goodreader.net/gr-man-tr-servers.html#sync