Yeah, it shouldn't delete the photos.
Go to the list of albums and such on the left side of iPhoto. At the bottom should be a trash bin. Go into it and see if the 1500 photos are in there. If they are, move them back to the Library.
Deleting doesn't actually get rid of them. If she emptied that trash bin, THEN she has lost her photos.
If she did delete her photos, then yes, tell her to stop using her computer until she uses Data Rescue. This will ensure that she doesn't overwrite her photos in the harddrive.