Our first daughter was born 8 weeks premature 7 years ago. What are the chances of having another premature birth?

You are at increased. Risk, please discuss with your OB and you should be followed closely by your OB along with a perinatologist that your OB chooses to help follow you, as now there are better meds to prevent premature labor and better methods to detect it.
Elevated risk. Women who have preterm deliveries are more likely than other women to have preterm labor again. You should discuss the use of 17 hydroxy Progesterone injections with your doctor as a preventative measure. You may want to ask how they manage prenatal care in women with a history of preterm birth to make sure you understand and agree with the plan.