When dogs tie it is like a 99% chance of pregnancy, she may have fallen into that 1%.....also if she was not in heat, or she was in her last days of being in heat, then her eggs were not ready to receive. Her not being pregnant after being tied does not mean anything is wrong with her or ur stud (unless u notice anything different about her) if she is acting the same, eating, drinking etc...then she is fine....it. just wasn't the right timing that's all.
Other people asked questions on various topics, and are still waiting for answer. Would be great if you can take a sec and answer them