If she's in transit from a combat zone to a non-combat one, it's plausible that she was required to turn in her weapons due to US military regulations. Being transferred to Frankfurt would definitely be a situation where she would not be expected to be armed upon arrival - it means she's being transferred to the military hospital at the base in Frankfurt, Germany, which is usually the first step for most American military before being transferred to Walter Reed Hospital and/or being processed out of the military.