There are states that recognize married domestic partners, if you live in one of those states and someday decide to get married, then that would entirely affect your credit score. But since you stated that you are not going to be married to her, the only way that her credit can affect yours is if you co-sign for any of the loans or any financial responsibilities that she might apply for. These could be car loans, home loans or joint credit and debit card accounts. If there is a need for you to be involved with her financial obligations, I suggest that you conduct a credit check
regularly so you can keep yourself updated about the effect of her financial activities on your credit score.