The girls in green were unable to match the level of performance they produced against New Zealand last week when they came from 11-7 down to beat the reigning world champions.
Rosser's half-back partner Nora Stapleton, who is playing at her second World Cup, said after the semi-final: "It's hard to explain at the minute because, personally, I'm feeling a bit numb. You don't really know where that performance came from. It was a huge contrast from the New Zealand game.
"At half-time in the New Zealand match we went in feeling confident and feeling we were very much in control of the game as well whereas this time we were: 'right, we have to turn ourselves around'.
"We went back out (for the second half) and we just didn't do it. Today just wasn't our day."
Rosser, who came out of retirement for the tournament, has experienced disappointing losses to England in the past and knows Ireland have to move on quickly in order to give Sunday's 3rd/4th place play-off against France their best shot.
"We have to stay positive. It hurts at the moment but when we wake up we have to go again and focus on Sunday," urged the 36-year-old veteran (pictured below).
"We need to park this game and move on because we can still finish third which would be a huge achievement. We set out to make the last-four but we really thought we could get to the final and give ourselves a shot at winning it."
Having leaked 18 points in the second quarter, it was vital for Philip Doyle's charges to answer back on the resumption but England kept a stubborn hold of possession and continued to wear Ireland down.
"There were no panic buttons being pressed (at half-time) or anything like that. We spoke about needing an early score in the second half but unfortunately we just couldn't get it," explained Rosser.
"They came at us hard and we found it hard to get a foothold. But when we wake up in the morning, we'll clear our heads and go again.
"We can't let ourselves or our supporters stay down about this. We're so grateful to everyone that travelled over and we know how well we've been supported back home.
"It's important that we get that third place finish. Irish women's rugby has come on leaps and bounds in recent years and it would be great to keep that going."
Donegal woman Stapleton echoed those thoughts as she hopes to make further history this weekend by securing Ireland's first ever win over 'les Bleues' on French soil.
Mindful of what such a result would mean for the Irish camp and the 'magnificent' travelling support, she added: "We know we can play much better than that and in four days' time we want to show people what we can do.
"When you are feeling numb or low coming out of a game like this it is nice to have another game. It is a huge game against top notch opposition."