Hi Jennifer,
I can recommend adding yoga to your regular routine. As a dancer you will have worked on your flexibility as well as stability in a very dynamic way. Having discontinued this and now taking up running, your body will indeed be at risk of getting stiffer very quickly even with the usual stretches that are recommended for runners. Yoga is popular but from experience it is also very effective on very many levels and from feedback it works well in combination with sports and dancing. I know a few people who are ex-dancers who are very happy having taken up yoga. I can highly recommend Iyengar yoga. It is cheap and with guidance from a teacher you can very quickly develop an own practice at home that you can enjoy for free. You will know your body well and have a good awareness so you can use yoga to help you counteract the developing stiffness in your hips and rest of your legs and anywhere else in your body (and mind)..