I think this is great! I am in love with your granddaughter! Except that I have the age difference to have her a a daugher ... ah ah :-)
I think is great she likes to tinker with stuff and understand how vehicles operate - makes you a better driver, or a driver, really.
My little one (3 to 4 this year) just sits on my lap and turn the wheel, but is ok. Already knows what screwdrivers and pliers are made for, and I think is a good thing.
I think the D1 300 is a good and balanced car, albeit a bit tractorish, and perhaps sluggish with the auto (is it mechanical injection or the late ones with EFI?). I remember mine fondly, lots of space, very versatile vehicle. I regret selling.
Watch for rust as commented, without sunroofs you got a (big) problem less to worry about.