Generally yes, but not in the way you think. It is not as if your credit scores will somehow be combined or averaged when you marry. In fact you'll both retain the your own scores and your own financial identities. However, you'd be smart to find out why your girlfriend has such bad credit before you get married. Regardless of her reasons,you need to keep your financial life separate from her's that means, no sharing or getting joint credit cards, no buying a house by jointly signing a loan, no jointly owned cars, etc. That is how her credit will harm you. Also in Ohio, insurance companies use credit scores to evaluate risk and price insurance products like auto and homeowners insurance accordingly. Her presence with you might mean you pay more for your auto or home insurance once you're married. If your girl-friend has substantial debts to go along with her poor credit, you might also want to sign a pre-nup agreement that lists all the debts of each of you and assigns them exclusively to the appropriate party. Although debts that you each have coming into the marriage are considered to be separate under Ohio law, laws change.
I'm not trying to be a kill-joy but these are all things to think about. Perhaps an hour or two hour session with a lawyer or credit counselor might do you both some good prior to you marriage.
