Shar Pei X Cattle Dog

Question
I have a Shar Pei x Cattle dog, she is 5 months old and is booked in to be desexed in a months time... During this time I have a family member coming from a different state with her Border Collie boy who is not desexed and humps EVERYTHING... My dog is not showing any signs of being on heat but I am not sure if I should tell this family member to not come over or not? Is she too young to be on heat? Or should I just keep him away? (better safe than sorry) could it be possible that she could get pregnant being 5 months and never in heat?

Answer
Samantha,
A female can come into heat anywhere from four months to two years.  I find that the larger dogs usually come into heat a little later, but that is not an absolute.    Yes, she could get pregnant on the first time, even being five months.  
Can you schedule her spaying a week or two early and have your friends come a week or two later?  That seems like it would cover all bases even the visit.
nancy