Contance Dykhuizen, an American visitor in her mid20s, went with her husband to watch the confrontation on Phichai Road when something exploded near her right foot. They tried to run for safety, but Contance found her right leg was bleeding and she couldn't move.
She was taken to Phramongkutklao Hospital.
This was her first visit to Thailand, arriving a month and a half ago.
The couple work as volunteers at the Education for Life Foundation in Phayao province to help provide education for northern children suffering from poverty, lack of parental support, child labour, prostitution and drug addiction.
"My husband has a journalism degree and we both like to travel and learn more about culture and politics. We went there to see what's going on," Contance said.
Both her legs and feet were wounded, her right leg severely.
Colonel Peerapol Pokpong, head of the hospital's Centre of Public Relations and Special Affairs, said she must stay at the hospital for two more weeks.
"Her wounds are now improved, but some are infected. Doctors are treating the infected wounds and will perform surgery to dress the wounds within two weeks. We have teams of physical therapists and psychiatrists to help her," the doctor said.
Contance agreed with critics who said the police should use better kinds of tear gas for crowd control as the type used on that day hurt people.
"I am very grateful for the government for taking care of me; but I find the situation with the tear gas very unfortunate," she said.
"It is unfortunate too that both sides have chosen to resort to violence and I wish that things could be more peaceful in the future for both sides."
Despite the bad experience, the two foreigners insist they still want to stay in Thailand to continue helping children.
They were afraid that if the violence continues, it will rebound on tourism here, as the flareups make people in their country nervous.
"We're telling everybody that it's very safe here - if you stay outside the very specific protest area," her husband said.