How many times does the word grandma appear in the Bible?

None, according to this website which is pretty comprehensive
http://www.biblegateway.com/quicksearch/?quicksearch=Grandma&qs_version=NIV

None, the Hebrew language doesn't even have a word for it. (Modern Hebrew stole the words "savta" and "saba" - for "grandmother" and "grandfather" respectively - from Aramaic.)

"Grandmother" appears once in English versions, in 2 Tim. 1:5.

"I have been reminded of your sincere faith, which first lived in your grandmother Lois and in your mother Eunice and, I am persuaded, now lives in you also."

Scrolling down to the bottom of the page,it also appears in the Apocrypha.

"Grandmother (μάμμῃ)

"N.T. Once in lxx, 4 Macc. 16:9. Later Greek. The correct classical word is τήθη. See Aristoph. Ach. 49; Plato, Repub. 461 D."

http://bible.cc/2_timothy/1-5.htm