The writer mates this dog regularly, but on the most recent occasion she did not become pregnant.

Interested in Language
Hi, all :)
I found this phrase in a novel (The Marked Son) and I'd like to know the meaning. I've googled it, but couldn't find one.
“Shelley’s my best breeder. I shouldn’t have left her, but she didn’t take this time around.
A million thanks for your help! :D
The writer mates this dog regularly, but on the most recent occasion she did not become pregnant.
Thanks a lot, 5jj and bhaisahab :) What a help!