If your GF wants to be up close to the lava on the Big Island, you can take the Poke A Stick lava tour. I took it in February and loved it. About a two hour walk to the lava, but so worth it! You can check it out at:
http://lavarefuge.com/poke-a-stick-guided-lava-tours/
The Big Island is my favorite island. There is a lot to see and do. Snorkeling with the manta rays is another fabulous experience. It is almost like being on a different planet.
http://www.bigislanddivers.com/mantadive.html
If you want to actually visit the Memorial in Pearl Harbor, remember the only way you can get there is via the shuttle through the National Park Service.
Have fun!