I have been working nights outside in Colorado for the last 10 years. I spent most of those shifts outdoors on foot. I haven't found anything that even comes close to the Army gen 3 ECWCS thermals
https://www.armynavyoutdoors.com/mil...UaAmIbEALw_wcB
I worked 11-7 last night. The temperature was 3 degrees. I was wearing the silk weight thermals under the Polartec "waffle tops". Because of uniform requirements I had on a light black sweater. Then my uniform shirt (probably made by the same company that makes your sister's uniform) BDU pants and a sweater similar to the ones the Army used to issue with the class Bs. I also had on a Polartec beanie
I'm not going to say I didn't notice the cold but I wasn't uncomfortably cold. I was able to perform my duties all night.
I buy mine from the surplus stores. I pay about 30 bucks for an entire set