Welcome to KnittingHelp! How kind of your grandmother to make this dress.
I'm not sure exactly where she's having trouble so if this doesn't help then just come back and ask.
There should be 85sts for the back.
Slip the first 46sts of the back onto a holder or thread. Start with a new strand of C yarn:
(k2tog, k1)x4 [that's k2tog, k1, k2tog,k1, k2tog, k1, k2tog, k1]
then (k2tog, k2)x6,
Now you're ready to work the 41 sleeve sts:
At this point you're up to the front sts.
As I said, I'm not sure how helpful this is so if your grandmother could tell us what the exact problem is, maybe we can try again. The numbers for the sts add up correctly.