Potential lels aside, that thing was a one-shot railgun we, um, 'borrowed' off one of her troops. They use them like RPGs.
The girl grabs the weapon with one hand, and pegs it at Barti. It weighs about 80 kg, so it doesn't hit softly.
38.5554 kg
38 kg by itself
58 kg with tripod and associated mechanisms
92 kg by itself
That single-use, situational weapon weighs more than pretty much any infantry portable weapon and approximately eight times more than its conventional equivalents which tend to weigh under 10 kg. Comparatively, the +10 Extremity Combat Railguns used by those WSC-PCS units are only about 2.8 kg.
For further reference, a 2001 Army Science Board study indicated that soldiers should carry no more than 22.6796 kg. Infantry in extended patrols in Iraq carried up to 57.6062 kg worth of gear, far higher than that guideline. These disposable, single-shot weapons weigh more than the entire equipment set of a normal soldier.
Furthermore, judging by the fact that Murder Night's rather poor human resources department seems to indicate that perhaps, she doesn't actually work that much with regular humans. Combine that with what appears to be a gigantic summoning seal in her compound, I have a feeling that her soldiers are far from what constitutes as a 'normal' human, or really, what constitutes as human at all.
Perhaps a good question to ask would be, how exactly do those soldiers look and act. Because I would presume they are carrying far more than just a single use weapon, in fact, their total gear weight probably weighs more than an automatic cannon designed for aircraft use. Which then leads to the question,
what the fuck are her entrenched weapons, the AA guns and heavy defenses? Because if their infantry carries that much, I'd hate to see what their artillery looks like.