My suggestion would be to give survival a try with plain old vanilla. They've updated the game with an incredible amount of new content, so you and your sister will find lots of new things to play with. Enchanting is always a fun thing to do, here are some suggestions for armor enchantments. You can also make it a goal to defeat the End Dragon or the Wither. And not to mention the Caves and Cliffs update is on the horizon which will bring a long overdue update to the cave system.
That being said, the mod community continues to amaze me with the content they create and add to the game. If you decide to run the route of mods, you absolutely want to check out CurseForge. If you are looking for some quick suggestions, here are few:
Horror Adventure Maps