She served the club for more than 50 years in various voluntary roles at Dudgeon Park. The 2-1 win saw the Highland League side eliminate the tournament's finalists of the last two seasons in a huge shock.
After what is the worst result in Hearts' history, manager Robbie Neilson admitted being devastated and said fans deserve an apology.
"It’s difficult to put it into words," admitted Mackay. “I’m just incredibly proud of every single player, and everyone that’s connected with the club. It’s just a monumental night for everyone involved with Brora Rangers
“I spoke about it before the game, and you just never know in football. If you go in with the right attitude and belief sometimes results can go your way. That’s what has happened tonight.
“It’s just an unbelievable achievement for the whole team and the whole club.
“There are guys like John Young, who has been a long suffering fan, kitman, chairman – everything under the sun. It’s guys like John and Sandy Matheson the groundsman that results like these should be dedicated to.
“We had Sheena Manson, a club servant who passed a few weeks ago and we did a minute’s silence for her tonight.
“I’d like to dedicate that result to Sheena because she was the heart and soul of the club for 40 or 50 years – and she is sorely missed.”
Brora hadn't played competitively since January 9 and only trained five times before facing Hearts after their league was suspended due to the Covid pandemic.
Neilson said the result was unacceptable and that his team had let their club down badly.
"We had a long conversation at the end because it's not good enough," he remarked. "The standards when you come here need to be miles better. You have a responsibility playing for Hearts.
"It's not acceptable. There will be players who step up and get the team going again and players who can't. It's up to us to have players here of a standard that we don't get that performance again. We need to make sure we win the league first and then we need to move the club forward.
"I'm devastated, absolutely gutted. Credit to Brora. They competed really well and worked really hard, some brilliant defending and threw bodies on the line. Ultimately, we were miles off where we need to be.
"We could go over it for the next six hours but it's not good enough – as coaches, staff and players. The only way to change it is to get back into training and get at it."
Asked if fans deserved an apology, he replied. "Definitely, 100 per cent. It's not acceptable at this football club. We have a lot of work, fight and hunger to show to get over this. We need to do it.
"We need to win on Saturday and win the league. We will remind them about this regularly to make sure standards are better and this does not happen again."