"The biggest challenge for me was going through the physical standards," she says. "I'm a small person, you know, the female standards are going to be the same as the male which they should be, but that was the biggest challenge for me."
This is more than just a title. She is responsible for a platoon of six. Their mission - to deploy high mobility artillery rockets.
"Yes, I shoot rockets, it's pretty awesome...you see it first and then you hear it and it's just nothing like it!"
Being the first came with some growing pains for her battalion.
"So I sat on staff hearing their different plans on how they are going to integrate females...how they are going to change the female restrooms, which was currently an office."
The Secretary of Defense ordered every branch of the military to have a plan to integrate women into combat roles by January. Last summer, two women graduated from the elite Army Ranger School.
Sergeant John Lemke is a retired Marine, now a Platoon Sergeant in the 1st Battalion. He sees great promise in officer Griener.
"Lieutenant Grenier has been one of the strongest platoon leaders that I have worked with. Learning the job, instructing the soldiers, and working with them," said Sergeant Lemke.
2nd Lt. Grenier encourages other women in the military to seek out these new opportunities.
"If that is what you want to do, go for it, because you're already in the mental mindset of going for it. And wanting to do great things and lead troops."
In the Wisconsin National Guard, women will now be able to apply for about 2,500 infantry and calvary units positions once closed.