McIntyre had snapped the photo of her sister Caty Nixon back in July but saved it until Oct. 10 before writing the sweet tribute along with the photo.
"Caty just wrapped up her fourth shift in a row. that's around 53+ hours in four days.That's not including the 1.5 hours she's in the car each day. She usually doesn't get a chance to eat lunch or even drink much water. (& she has to dress like a blueberry.. i mean, come on)," the caption read in part. "She is so good at what she does that she often forgets how to take care of herself while she's taking care of her patients."
The night the photo was taken had been a "particularly hard day" in which Nixon had delivered a stillborn baby, McIntyre wrote.
The post has been shared 86,000 times, with most of the comments written in support of the amazing work nurses do every day.
"I don't like being in the spotlight, and I love that Laura wrote a tribute to not only me - but to all nurses - for our passion and dedication, even through the roughest days," Nixon told "Good Morning America."
The job is filled with highs and lows, she said.
"The best part of nursing is making connections with people, being the calm in the storm, being their cheerleader when they need encouragement, and being the shoulder to cry on when they are hurting," Nixon told "GMA" in an email. "The worst, though, is knowing that even when you've done everything you can for someone, we're not able to change the outcome (for fetal loss, poor prognosis, etc.); always feeling like you have to be strong for your patient - when on the inside, you are falling apart."
Nixon thinks the post has touched so many because of the "raw emotion" her sister captured.
Nurses deserve every ounce of recognition they get, McIntyre said. "They are the heartbeat of the hospital, and they are truly angels on earth."