Hi and welcome! I'm also a grandmother. I found this site 8 years ago when I was becoming a grandmother for the second time.
There's a bunch of great convertible seats available that will rear face your granddaughter for quite a while. The NHSTA recommends rear facing until the convertible seat is outgrown.
http://www.safercar.gov/parents/RightSeat.htm
The new Graco Size4Me 65 is attracting a lot of attention for it's long rear facing capabilities as well as it's long lasting forward facing use. It's pretty new so there's not a lot of information out there yet.
Some other well liked convertible seats here are the First Years True Fit, the Evenflo Triumph Advance 65, the Graco My Ride 65 or My Ride 70 to name a few.
Here's a link to a video showing why rear facing is safer.
[ame="http://www.youtube.com/watch?v=sssIsceKd6U"]Rear facing vs forward facing position in the car - YouTube[/ame]