Your concern is valid if you are using the same software and PC to transfer files from both cameras (notice I said PC, not Mac - I don't know about Macs). You must first determine if both cameras use the same naming convention. If so, then you will need to determine how you want to store pictures to ensure they are located in separate folders. If they have a different convention, this should not be a big problem.
E.g., if you camera uses the convention IMG_xxxx.jpg (where xxx is the numbering), then the transfer software may put your files in a folder called My Pictures | Canon | 01-10-2007 so you would have something like this:
C:\Documents and Settings\eeyoreforever\My Documents\Canon\01-10-2007\IMG_0001.jpg
If your daughter's camera used the same naming convention and she shot pictures the same day and she used your logon to the computer, then her files will be put in the same place and, if the filename was the same, it could overwrite your image.
Now, if her camera used the convention IMAGE_xxxx.jpg and everything else was the same, then you would have something like this:
C:\Documents and Settings\eeyoreforever\My Documents\Canon\01-10-2007\IMAGE_0001.jpg
which would not overwrite your image.
If your daughter logs onto your computer using a different name (this assumes you have your computer set up for multiple people) then it does not matter if both cameras use the same naming convention. The images will be stored in separate places on the computer. If your daughter' logon name was Dorthy, then her images would be stored something like this:
C:\Documents and Settings\Dorthy\My Documents\Canon\01-10-2007\IMG_0001.jpg
while yours would be
C:\Documents and Settings\eeyoreforever\My Documents\Canon\01-10-2007\IMG_0001.jpg
Notice that although the image name is the same, the location is different.
Now, if you need to save them to a CD or DVD, then again, you must be careful not to overwrite images that use the same naming convention. You would want to keep yours on CDs separate from your daughter's.
I'm sorry if this is long-winded, but there are alot of possibilities when computers come into play.