My girlfriend wants to go on vacation

Go to Ocean City New Jersey! I think from Columbus it would be about 8-10 hours to drive. There are a lot of things there for kids to do and they can see the ocean!
Ripley's Believe it or not Museum is the BEST! It is really fun.

First choice would obviously be Beaches resort. It may seem a little pricey upfront, but you have all meals, all entertainment, free daycare during the day should you want some alone time and all drinks (including alcohol). By the time you add it up for all four of you would spend way more than that in a less fabulous place!

http://www.beaches.com/

You can look on their calendar to see some cheaper times of the year to go.

I also remember a commercial for Disney World that was air, hotel and all three park passes for $1400 for the week - which is a great price!

Mexico is always a good option too - just remember to get their passports!

How about a road trip to North Carolina?

Myrtal Beach South Carolina, my kids loved that when they were little! (they still call it "turtle" beach) It's fairly inexpensive, you can get 3 days and 2 nights as low as $99, and that includes a dining card. There are boardwalks, and amusment parks, and water parks, and of course, a truely awesome beach to play on.

http://www.mbchamber.com/

http://www.exclusivegetawayvacations.com/myrtle-beach.php