I would worry about possible pyometra.
If you want to try to save her for breeding purposes you could try prostaglandin treatment instead of spay.
The infection may be the reason she did not conceive.
You can read about this and treatments here
http://marvistavet.net/html/body_pyometra.html
You might want to test her for brucellosis if she and the stud were not tested before breeding too.
Maybe this is just a vaginitis, maybe its a urinary tract infection issue but I'd be worried based on the timing about a pyometra.
Hope this helps you!
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