Rogne vs Rognehaug

I am new at researching my Norwegian ancestry. Both of my maternal grandparents emigrated to the US and settled in Minnesota. I have found my grandmother, Tena Rogne, listed on the Ellis Island website as Torstine Rognehaug. Her siblings who emigrated also used the surname Rogne. Help! How do I research her family? I know she lived in Bergen and came to the states in 1917. I would love to know about her parents, etc. Thanks!