At the age of 13 she was using drugs. Three years later she was expelled, written off by her school as “a borderline personality disorder, criminal, on my way to prison”.
Ms McGrath went on to a successful career in the charity sector, but she has never forgotten what it feels like to be someone that society has given up on.
Chance UK, the charity she has run since 2001, provides a successful one-on-one mentoring programme for children in aged five to 11 with behavioural difficulties.
On the anniversary of last year’s riots in English cities, there has been much focus on the young people who looted and burned their own communities.
But as Ms McGrath points out, “you don’t suddenly wake up at 14 and decide to carry a knife and rob a shop”.
“Anyone working in primary schools will tell you there are children who are getting into trouble, who are being excluded from school and who then feel education is not for them, who feel there is no way out. Their world, their chances of growing up and getting a job, start to shrink at an early age.”
The young people rioting last summer “were crying out for help when they were at primary school”.
“Why not work with them when they are asking you for help?” she asks.
Those children at risk display a range of behaviours – a propensity for violence, a feeling of exclusion, no sense of right and wrong, getting so angry and frustrated that they cannot control their emotions.
“Those children will continue feeling angry and excluded,” explains Ms McGrath.
Chance UK provides tailored one-to-one mentoring with a carefully screened, trained and supervised volunteer mentor.
Those mentors then work to raise children's self esteem via activities such as sports, visiting museums, making scrapbooks or whatever the child may be interested in.
The riots were a wake-up call for Whitehall and Westminster, but more unrest is not inevitable.
Ms McGrath says any sense of inevitability “makes people feel helpless”.
“You can do something to prevent it and that is learning lessons from why it has happened, working with disillusioned families and early intervention,” she says.
“The youngest child arrested was 11 years and six months. Primary schools children were not affected in the sense they were not out on the streets being arrested, but it made them very frightened.
“Soon they will feel the pressure to participate and we need to give them the courage to stand up and know the difference between right and wrong.
“I have done this job for 11 years, working with exactly the same type of kids, but the environment has changed.
"Then we did not have gang problems or people being killed on the streets and even five years ago primary school children were not targeted by gangs, but now they are.
“Kids are now witnessing things that cause post-traumatic stress. They might be caught up in a tiny little war between two gangs, but they are seeing real violence and sometimes that is replicated at home.
“Their houses are being raided for something their siblings are suspected of doing.”
Primary children may not have been out looting and rioting last summer, but they saw adults who should be role models, parents and neighbours and older siblings, participating.
“It was anarchy and chaos - kids don’t like that, it makes them scared of the lack of control and fearful of what happens next.”
The London Olympics have been a bright spot in the lives of many disadvantaged children in the capital.
“Children see people from their communities succeeding who have worked very, very hard. That is incredibly positive. It is great to see how seriously those people who own medals take their responsibilities as role models. They are the exact opposite to the role models some children see, people who sold some drugs and bought a flash car.”
In London Chance UK can fund 180 mentors a year
“We could easily work with double that number and the only thing that is stopping us is the money,” says Ms McGrath.
After last year’s violence, politicians decided that action was needed. They have held inquiries and produced reports. Now it is time they “put their money where their mouth is,” says Ms McGrath.
“We need to move away from talking about supporting early intervention to financially supporting it.
“I know we are in austerity but what will make us poorer in the long run is more children taken into care or the criminal justice system, destroying those children’s lives and futures.”