The combat medic will take up her post in the summer.
She has previously served on operational tours of Iraq and Afghanistan.
"I think there is still a time and place for that [stereotypical angry, male Sergeant Major] depending on the situation," said WO2 Caswell-Treen when discussing how women soldiers are perceived within the Army.
However, she also believes that with the training and leadership style offered by the Army equality in terms of skill level is possible:
"We have every tool in our toolbox to perform well whichever the circumstances."
"It is great that we [the Army] have lowered those [gender] boundaries that once were there," she remarks while also praising the British Army for being an "equal opportunities employer."
"If you have the capability and standard to perform at the required level, I don't think there should be a barrier."
WO2 Caswell-Treen has also been serving with 4 Armoured Medical Regiment in Aldershot and applied for the role at Sandhurst when the post was made available to women last year.
She says the hardest time in her Army career so far, has been serving as a combat medic in Sangin, Afghanistan between 2007 and 2008 - she looked after civilians and the Afghan National Army, as well as her own colleagues.
"The more campaigns that you do and the more warfare adapts," reveals WO2 Caswell-Treen, she is aware that those are not the situations she would like to find herself in again.
"The level of medical care we give to personnel is something to be proud of," she says.
"I'm very proud of what I've achieved as a medic."
Originally from Uttoxeter, Kelly followed her father into the Army after growing up on various bases, including Germany.
WO2 Caswell-Treen told Forces News she was thrilled to pass the six-week selection course and will take up her post in the summer.