By all means have a preg /health check if she is that valuable. I have seen cows "come in heat" and they were bred.
On the other hand, I have seen cattle health check out fine, and they wouldn't breed, or they would breed and slip the calf and then start all over again, and no understandable reason could be found. Eventually they were given horomones and are now in calf.
One has to decide how valuable the cow is, and through that decide how long to keep trying or ship out.
That said, if the cow is in a very large herd and only one bull, he might be chasing another cow in standing heat during the brief time that your cow is standing, and miss her.
Nite Hawk