The Arsenal Ladies midfielder was the girl at the centre of attention in Belfast, where the Lionesses replayed the final 16 seconds of their Euro Qualifier with Norway.
Instead of correctly ordering a re-take, Norway were awarded a free-kick, thus denying Mo Marley’s side what would have been a crucial point in the Elite Round stage.
Thursday's replay began with the penalty and Williamson held her nerve to level things up before the final whistle sounded seconds after Norway had re-started the game to ensure England are heading to the Euro Finals in Israel this summer.
"I have experienced every single emotion over the past 24 hours," admitted Williamson after the game.
"But it wasn't about me, it was about the team. I know everyone says that, but it really was, and I have never felt calmer than when she blew that whistle.
"We had a job to do, we did the job and we took an opportunity that I would never have dreamed to be gifted.
"It's incredible and my mum managed to change her flights home so she could stay and watch. That was really nice."
It ended an eventful day for England, who had played their final group game with Switzerland earlier in the day which ended in a 3-1 win.
Williamson was on the mark again in that game with another penalty, which warmed her up nicely for what was to come later.
But the current England Women’s Youth Player of the Year admits she had no problems relaxing ahead of the Norway replay a few hours later.
See the equalising penalty from Leah Williamson in England's replayed game with Norway
"I went for a sleep," she revealed.
"There was nothing else to do. I was pacing around last night so I didn't want to do that again."
Marley and her team will now begin planning for their trip to Israel in July. The draw for the Finals is made on 20 May, with Israel, Germany, Spain, Denmark, Norway, Sweden and France all involved.