There is only one target remaining when you win a Commonwealth Games silver medal and Glasgow 2014 offers her that opportunity.
It matters not a jot that she will be 50 by the time the Games come around. Just a few minutes in her company and you are aware of her single-mindedness.
Single-minded enough to sell her prized herd of Aberdeen Angus cattle five years ago ("that broke my heart") to enable her to train harder.
Single-minded enough to put herself through four hours of shooting a day in addition to the gruelling strength and conditioning sessions to keep her in the peak of condition.
Single-minded enough to come back after 12 years away from the top level of the sport, to win a place in three Commonwealth Games teams, her place at Glasgow 2014 now confirmed.
The farmer from Alford, Aberdeenshire, is adamant she will not compete internationally after the Games, the priority being the gold medal. After that - win or lose - she will move in a new direction, one which she herself is as yet unsure of.
She has already concluded the sale of her farm but hopes to still be able to remain there for the next nine months, to use the three traps she constructed on the land to plot her assault on the rest of the Commonwealth. The shooting is almost a local event for Marshall, taking place at Barry Buddon, near Carnoustie.
"Having home advantage is really important even though we are not going to have that much access to Barry Buddon beforehand," she says. "Just the fact we don't have the travel issues, we know the weather and we know the people - it will all help.
"Having the shooting located there, there are disadvantages to being a bit remote from the main activity in Glasgow. But, from a weather perspective, it could be a bit drier on the east coast, although I think it could be a bit windy which might cause problems. But I'm used to shooting in windy conditions so hopefully, I can use that to my advantage.
"It's almost like being in a bubble and you can really cut yourself off if that's what you want. I find that really conducive because you're there to do a job and there are no distractions so you can get stuck in.
"The shooting events are going to be over quite quickly so we can then go back to the village in Glasgow and really enjoy the rest of the event."
The foundations will be laid by a heavy volume of training from December to February and, having had her selection confirmed last week, Marshall can now pick and choose which international events will best serve her build-up to the Games. She insists the high volume of shooting - between 150-200 targets a day - did not disturb her cattle.
"That's not the reason I got rid of the cattle, they were not bothered by it at all," she says. " I have roe deer come out in the fields behind me when I'm shooting and they're quite used to it. They know I'm not aiming at them!"
Marshall retired from top-level shooting to have a family (daughter Katy is now 29 and son David, 27) and it was only after watching the 2002 Commonwealth Games in Manchester that she decided to attempt a comeback.
"I didn't miss the shooting per se because I was travelling on my own and the children were at home but I missed the people, because they are a great bunch of folk. I didn't really expect to get back to this sort of level but as soon as I took the gun out again, that was me hooked, absolutely.
"I set Melbourne 2006 as my target and I qualified for that and I was disappointed to just miss out on the final. I just worked towards Delhi and that [the silver medal]has been the highlight of my career so far - it's always great winning for Scotland. Even when I'm in a GB vest, I'm still a Scot and that's important to me."
Marshall is aware that shooting has its critics but staunchly defends her sport: "I used to be very wary about telling people I did shooting but it got to the point where I thought why should I be ashamed of my sport?
"I give up as much time as any other sportsperson. Just because I don't have the physical attributes to sprint 100 metres in 10 seconds does not mean I'm any less worthy."