
I'd wait until day 30 for a scan and if you can find a home scanner, do that instead.
Day 26 is when scanning is recommended but my scanner says 30 is best as unless you're progesterone testing, you have no idea when she ovulated. A later mating will mean day 26 is too soon.
We had an awful experience at the vet, where they shaved my girl too close - resulting in razor burn, they kept forcing her to lay down and then spent two minutes looking before declaring she was empty. She was and they were right but the whole experience was so traumatic that I've always had the scanner come to us instead.
At home, we aren't rushed, she gives an approximate head count, can tell which is the mating that most likely took, let's you make videos and take pictures at a fraction of the cost!
Fingers crossed for you and your girl x