maltese bitch

Question
Hello
I bought my maltese bitch at 9weeks and she would bring up her food at least once a week ,sometimes more.When she came into season at 12 months.3 weeks after her first day of bleeding she got really sick and dehydrated quickly,My vet said i got her to the vets just in time to save her.He thought it was a gastric infection and put her on 1ml protexin everyday,and a muschy diet.
My bitch was better a week later.Then when she came into season again 6mths later , It happened again she got really sick exactly 3 weeks after her first bleeding day, but this time she couldnt fight for her life and died.
Why would she only get really sick when she was in season?

Answer
She could of had a uterine infection, which can be life threatening.  Did you ever have any blood work tested?  There could have been an underlying problem such as liver disease (or liver shunt), kidney disease, Addison's Disease, blood sugar abnormalities.  Without an autopsy it is hard to say.