On Saturday morning, about 80 people joined the search for Kirkpatrick, whose husband told deputies they became separated while walking through the forest at 8 a.m. Friday.
Deputies confirmed Kirkpatrick's body was found just before 11 a.m. on Saturday.
Her family has started a Go Fund Me to pay for funeral expenses.
"She helped raise me and my brother. She was like a second mom," Kirkpatrick's brother, Mike, told Eyewitness News.
"She don't go out in the woods, hiking or out of her yard. Her medical condition won't allow it. She's lucky if she can take the heat 30-40 minutes at a time," Mike added.
Lt. Scott Spencer told Eyewitness News the investigation is still active, and that foul play has not been ruled out.
Spencer said Allen Kirkpatrick, the woman's husband, is being questioned along with other family and friends.
Back at the forest, a forensics team is at the scene and a command post has been put up where it was first erected last night.
It's not immediately clear where in the forest the victim's body was found.
EARLIER TODAY: Search resumes for missing woman
DPS helicopters were searching the area, scanning for heat signatures on the ground. K-9 teams were also being used in the search.
The Montgomery County Sheriff's Office said the couple went looking for a dirt bike on Friday that had either broken down or was stuck Thursday night.
"At some point, Mr. Kirkpatrick lost sight of his wife," Captain Bryan Carlisle said. "She is...diabetic. She might have passed out, she might have fallen, we're not completely sure right now."
Woman reported missing in Sam Houston National Forest
Investigators said Theresa's mother last saw her daughter at 5:30 a.m. on Friday.
Allen was taken to the hospital to be treated for symptoms of heat exhaustion while deputies continued talking with him. Theresa's husband is still in the hospital due to dehydration.
Investigators weren't sure how long Theresa Kirkpatrick was without her insulin.
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