You don't need to apologize but you do need to not type in capital
letters. On Usenet - where you are posting - typing in all caps
represents shouting, is considered rude, and makes your post hard to
read. I know you didn't know this so I'm not scolding you; just telling
you for the future so other people don't yell at you. :-)

Ask your sister what she sent you. A good place to research file
extensions is www.filext.com. Here is a link to what I got when I
searched for ".mix":

http://www.filext.com/detaillist.php?extdetail=.mix&Search=Search

As you can see, there are quite a few choices. How you get the file and
with what you open it depends on what program was used to create the
file. Ask your sister and if you need more help, post back here with
her answer.

Malke

MIX is the file extension for the Picture file associated with Microsoft
PhotoDraw 2000 and Microsoft Picture-It! It is also the file extension for
Command & Conquer game package file.
Source:
http://www.liutilities.com/products/winbackup/filextlibrary/files/MIX/

Ask your sister to save the files in a format you can open (e.g., JPG) and
send them again, or seek help in a Corel Photo newsgroup or forum (e.g.,
http://www.tek-tips.com/threadminder.cfm?pid=240)