Grandmothers are so special.
I think that the temperature that the glass is heated to would be crucial. It may take some trial and error. And be careful. I couldn't find anything on Google.
I am not sure that current glass bottles are of the same type as your grandmother used.
I have used silicon carbide sand paper to smooth pieces of sharp glass, so that I could glue them to a rock. Be really careful with this also. I wore heavy welding gloves.
I also have read that pieces of broken glass can be smoothed off in a rock tumbler (polisher).
Heating pieces of glass in a kiln can also make the edges slump.