Females in heat

by Eimear
(Ireland)

Hi, I have a miniature Jack Russell Terrior named Lily. She is nearly 2 years old. I have read on a lot of different websites that they should come into heat every 6 months. My dog is an outdoor dog. I haven't ever seen any blood or signs that she was definitely in heat. The only time we thought she was in heat was when a male dog randomly came over and they were playing together but we saw no blood. Is it possible that she might not come in heat? We really want her to have puppies. What should I do?