Etherington had crashed in her practice run on Thursday, which proved to be her last after the final practice session was cancelled on Friday morning to preserve the course, but she showed no sign of nerves as she hurtled down the course at a top speed of 108kph.
Her silver medal was Britain's first at a Winter Paralympics since Turin 2006 and first on snow for 20 years. Team-mate Kelly Gallagher and guide Charlotte Evans finished sixth.
Lincoln-born Etherington, 23, a trainee teacher, couldn't have wished for a better start to Sochi 2014 with something to show already from her debut Paralympic outing.
"I can't believe what's just happened. We knew it was a solid run because we were shouting 'go, go, go' and we had good, solid communication," she said. "I'm so proud and excited and I can't wait to get that medal in my hands. It all came together and I think just the last year has proved how well we've developed. My skiing has improved so much and the team and Caroline are so supportive whether I'm skiing well or having a bad day.
"I think it really works and we're just really honest with each other. If something's annoying us or we're happy about something we build on from that. That was actually only the third downhill we've ever done together, but I knew we could do it."
While Great Britain's quest for Paralympic wheelchair curling gold opened with defeat, skip Aileen Neilson was confident her team of Scots, comprising Bob McPherson, Gregor Ewan and Jim Gault, could take heart from a promising start, and is convinced they can bounce back today when they face Sweden.
Beginning the round-robin stage against arguably the toughest opposition, ParalympicsGB held their own to take a 3-2 lead after three ends.
But an error from Neilson in the closing stages of the fifth end - which gave Canada the steal - proved crucial and the current world champions scored in the three remaining ends for a 6-3 win.
"Canada had the opportunities and some they took and some they didn't either, but we just have to focus on ourselves and not worry about the opposition," Neilson said. "We're feeling confident. We've played Sweden a lot and if we can come out the way we did this morning, very focused, very confident, then I'm sure we can have the same good start.
"We worked really well on the ice. For a few of the guys, it's their first Paralympics and I think that they put in an awesome display out there. They were very supportive of me and we had great team dynamics."
Seated skier Anna Turney was also in downhill action, but crashed out during her run after failing to stay upright on the bumpy course. But she refused to blame the conditions, instead signalling her intent to continue pushing the limits in search of a first Paralympic medal.
"I really wanted it and at the end of the day, I think I got the line slightly wrong, it was so bumpy and I just popped out," said Turney. "I am alright. I bounced a bit. My neck will stiffen up because that usually happens after a big crash like that, but I think I am fine. I have four more chances. Two more speed chances, so that is good for me."
Sainsbury's is a proud long-term supporter of the British Paralympic Association and a champion of inclusive sport for all. For more information on Sainsbury's commitment to inclusive sport visit: www.Sainsburys.co.uk/activekids