The wheelchair sprinter from Nanoose Bay, B.C., took silver in the T52 100 metres Wednesday after winning the 200 metres earlier in the Games.
"Unfortunately I don't get to hear O Canada and sing it as loud as I did the other day," Stilwell said. "I gave it everything I have and silver is nothing to be disappointed about."
Hers was one of four silver, but no gold, by Canadian athletes on Wednesday.
Wheelchair racer Brent Lakatos of Dorval, Que., was second in the T53 800 metres for his second silver at the track.
Benoit Huot of Montreal claimed silver in the S10 400-metre freestyle to complete his set of gold, silver and bronze so far at the pool. Montreal's Aurelie Rivard also won silver in the women's 400 freestyle.
Canada's cycling team also won its first medal of the Games with Marie-Claude Molnar of Lemoyne, Que., taking bronze in the women's C4 road race.
Canada improved to 21 medals in total with four gold, 11 silver and six bronze. The team's objective in London is a top-eight finish in gold medals. With four gold, Canada was tied for 20th and well off the pace of 19 won at the 2008 Paralympics in Beijing.
Stilwell was the gold medallist in both the 100 and 200 metres in Beijing. She aimed for repeat performances in London. Her T52 classification is for quadriplegic racers.
Her left hand slipped on her opening stroke of the 100. Belgium's Marieke Vervoort took advantage of the mistake and held the charging Canadian off for gold in a time of 19.69 seconds.
Stilwell followed in 19.80, which was well off the world record of 18.67 she'd set in Windsor, Ont., in July.
"That wasn't my best race," she said. ""Unfortunately just not a great start. I wish we could have a re-do, but we can't."
The 38-year-old had beaten the Belgian to win the 200 metres Saturday. Stilwell dominated her competition after Beijing, but Vervoort was an unknown quantity to her.
Stilwell says Vervoort was re-classified from a T54 - which has more arm movement - to a T52 in May.
"These are the first races I've ever had against Marieke ever," the Canadian said, who refused to argue with the decision to re-classify Vervoort.
"I've been asking for a long time for people to step up their game and give me some competition, so there it is. Kudos to her for coming out today and having the race of her life. Really, that's what it takes to beat me."
Lakatos closed hard, but couldn't catch Richard Colman of Australia for gold in the men's T53 800 metres. Colman finished in 1:41.13 ahead of the Canadian in 1:41.24.
"This was a little bit of a tactical race, but it was still fairly quick," said Lakatos. "The 800 isn't my strength. I'll take a silver any day of the week."
He also won silver in the 400 metres with the 200 still to go Friday.
Huot now has a swimming medal of each metal in London. Born with club feet, he races in a classification of minimal physical impairment.
The four-time Paralympian won gold in the 200 individual medley in world-record time on the first day of swimming. He also took bronze in the 100-metre backstroke. Huot races the 100 freestyle Thursday.
He was second to 16-year-old American sensation Ian Silverman in the 400 freestyle.
"I came here to do best times and I’m three out of three," Huot said. "I made good decisions coming here deciding not to swim the 50 free and the 100 butterfly because they would have been hard for me to finish in the top-five. So far it's worked. The events I've entered I've been on the podium."’
Rivard, 16, lowered her Canadian record in the 400 to four minutes 36.46 seconds. Elodie Lorandie of France won gold in 4:34.55.
"Elodie is always about 10 seconds ahead of me so to cut into her lead and win the silver gives me great pride," Rivard said. "My strategy was to save my energy for the end."
Molnar ensured the Canadian cycling team didn't finish the opening day of road races at Brands Hatch without a medal by finishing third in her 16-kilometre event.
"This is a tough course, so it hurts as it is supposed to," Molnar said. "This medal takes the pressure off the team."
Elsewhere Wednesday, Patrick Anderson of Fergus, Ont., led the men's basketball team with 16 points and 14 rebounds in a 77-51 quarter-final win over Spain. The Canadians face host Britain in Thursday's semifinal.
The men's rugby team didn't fare as well in their opening game of the tournament and fell 64-52 to Australia. The women's goalball team lost 2-1 in a quarter-final to Finland.