You nailed it. The woman was his fianceé, Whitney Mitchell, and was a quadruple amputee due to septic shock. Garrett’s mother, Sheila also said that Foster and Mitchell had been together since they were 17 years old.
https://www.dailymail.co.uk/news/article-8561833/PICTURED-Protester-shot-dead-Austin-protest.html
One 19-year-old teen from Richardson has kept up her hope after getting an infection that left her a quadruple amputee. The unimaginable happened to Whitney Mitchell. An infection led to the amputation of all her limbs.
https://www.dallasnews.com/news/2012/04/28/quadruple-amputee-files-lawsuit-against-doctors-medical-city/
Thanks for the links. That is a sad story. Some sources say he was an Air Force vet. Who knows what made him decide to get mixed up in all this trouble and to bring his girlfriend along.