I wouldn't worry. You two should be pretty safe. The only way she could have an STD without sexual contact is if her mother had it, and passed it onto her during birth, or if she's been using drugs like heroin that involve using dirty needle.
I wouldn't really dwell on it if she's clean and her mother's healthy.
Information on this site is provided for informational purposes only.
It is not meant to substitute for medical advice provided by your physician or other medical professional.
If you have or suspect that you have a medical problem, promptly contact your physician or health care provider.