"We were going over the photos my friend Ed Sanchez took (and) we discovered that gem with her sweet reaction.
"It really made that photo even more special."
Ms Rodriguez's brother Carlos Jair posted the photo on Twitter and it has gone viral, getting more that 53,000 retweets and 150,000 likes.
Even 50 Shades of Grey writer EL James retweeted it and congratulated the couple.
Ms Rodriguez, who is a second-year law student, said her fiance was a fan of the books so she freaked out when she saw James' comment.
"(We) definitely were not expecting that, or the amount of people that gathered in the gallery to watch and clap for us. It has been quite shocking and something we are not used to," she said.
She said 95 per cent of the reaction had been positive, although 5 per cent had been homophobic or objectifying comments.
"I think we are making progress in the world to be more accepting. We definitely appreciate that," she said.
"We have loved every single sweet comment from around the world."
Ms Rodriguez said in an Instagram post she chose the gallery for the proposal because of their love for art.
"If someone could describe our love it could only be done through a work of art," Ms Rodriguez wrote. "It is happy, fun, chaotic, inspiring and strong.
"I want to keep discovering art for the rest of my life by your side."
The couple met over blogging site Tumblr in 2012 and initially dated long distance for about six months but broke up because it became very difficult.
"Things were never the same and when I was almost done with my undergrad degree and with the flexibility to move anywhere I reached out to her," Ms Rodriguez said.
"I told her how I still felt about her and she felt the same way. Since that day we've been together ever since and have now lived together for almost two years."
The couple has been living in Chicago together and hope to get married in Texas in a year or two.
When asked why it was so important for them to get married, Ms Rodriguez said: "As someone who will soon become a lawyer, it is very important for me how something is viewed under the law.
"Having now the right to marry is just so important and is a step to show that in this country we are making progress to see LGBT people as humans and not second-class citizens.
"We plan on having a family and want our children to grow up to feel equal.
"With two married parents, who committed to each other under the law and under a spiritual ceremony.
"It's really no different than why a straight couple would want to get married, you know. To show commitment to one another and share the rest of their lives together."
Ms Rodriguez said she would love to thank the woman in the photo for making the proposal that much sweeter.
