The 42-year-old added the gold in London to the titles she won in this event in both 2004 and 2008.
Bruhn led from start to finish to touch in 1:35.50, 11.69 ahead of Song Lingling of China, who set an Asian record.
The USA swimmer, who made her debut in Athens aged 12, set a new Paralympic record of 2:37.09, 4.70 ahead of Russia's Olesya Vladykina.
Long said: 'She really pushed me in the last 50. I didn't think she would push me that hard.
'But as soon as I won the race she came up and said, "you're the best" and that meant a lot. It's a healthy Games. We all have the same goal.
'We all want to win, but it's really great and awesome when a competitor comes up and hugs you at the end of a race.'
Meanwhile, Ollie Hynd stood proud at the pinnacle as Great Britain claimed six medals at the Aquatics Centre, the teenager winning gold in the 200m Individual Medley - SM8, although his brother Sam just failed to join him on the podium in fourth place.
'It is more than I could have dreamed could ever happen at my first Games,' said Ollie Hynd. 'I didn't really want to believe I'd won until I'd seen the board.
'I touched the wall and saw the one next to my name and realised I'd won. I wanted to see it to believe it.'
Ian Silverman claimed the men's 400m Freestyle - S10 title, with Elodie Lorandi winning the women's equivalent.
Lim Woo-Geun picked up gold in the men's 100m Breaststroke - SB5, and there were wins for Aleksandr Nevolin-Svetov/Oxana Savchenko (men's/women's 100m Backstroke - S12) and Yevheniy Bohodayko/Viktoriia Savtsova (men's/women's 100 Breaststroke - SB6).
Yang Yang and Feng Yazhu prevailed in the men's and women's 50m Backstroke - S2 events, with Matthew Cowdrey and Lin Ping successful in the 50m Freestyle - S9 events.
Gustavo Sanchez Martinez clocked a time of 1:24.28 to win the men's 100m Freetsyle - S4.