All carseats can be installed with just the seatbelt.
Latch isn't safer, it's supposed to be easier(and that isn't always the case).
The radian65 is a very narrow seat. It can be a tricky install though.
You also may want to consider the Cosco Scenera...it's $43 and change at Wal-mart. It's pretty narrow and an easy to deal with seat. be sure to read over the car seat section of your car manual AND the car seats manual. If your seat belts don't lock, you'll need to use a locking clip. A car seat tech can help you learn how to do that.
I also reccomend leaving your granddaughter
Rear Facing. It's 4x safer than
FF.
Susan