You can put multiple photo's in an email using the share menu by selecting more than one photo. You can select multiple photos by holding down the Apple Key, next to the space bar, and clicking on the images you wish to send.
Dragging and dropping photo's from iPhoto should work. You did not mention what, if any, error message you received when your daughter tried to open them. It is not unusual for Win machines to not recognize the file type, for some reason, but if your right click the file and choose "Open with" and use the program you would normally view JPG files in, all should be well.
Hope this helps
My daughter has an XP puter and I have a mac mini with tiger. I drag and dropped some jpeg photos from iPhoto and she was unable to open them, 4 photos. So I went to share and sent them one at a time and she could view them. Is this normal? Also can you put more than one photo in an e-mail using the share menu?