Granny
Grandma, Old Lady, Old Woman
An old woman is who this is. Then, you add ちゃん for the name ender. You add お to be nicer. This person is a granny or grandma or old lady or old woman.
おばあちゃん
The reading isn't the ば you learned with the kanji. It's a slightly longer ばあ, because you gotta be nice, you know? Also, the person you thought was a granny is actually a sheep. Baaaa! (ばあ).
お婆ちゃんに、嘘をついたことで責められた。
My grandma accused me of telling lies.