Crystal's daughter has gotten into gaming with Minecraft and she's at the point where she wants to do mods. She doesn't understand it, though. Leo says that some mods run on servers online, while some go on the computer (called Clients). A good option is Gary's Mod. Some of the mods she's interested in probably aren't able to work on her computer, though. Mods also tend to work on PCs. The version of Minecraft on Mac runs on Java. There's also an iPad version, but she wouldn't be able to merge them. The risk with a mod, though, is that it's third party. The problem is that mods are often poorly written and that could be a security issue.
OMG Chad has a great youtube channel called OMGCraft that talks about Minecraft and how to install the mods safely. Leo recommends subscribing to it. A good computer for her at this stage is a Raspberry Pi. She can not only learn to play the game, but also how to do programming within Minecraft. It's a great way to learn programming.