Yeah, but she's supposed to get a sore throat if she uses it too much. In the manga (and first anime) she wore herself out summoning one large artillery piece (a WWII-era railgun.)
Unfortunately the people who did the OVA just decided to throw power levels to the wind. This scene makes me sad.
It's a Railway Gun not a Railgun. Those two are different things but the Nazi really did tried to make a Railgun. She summoned forth a Schwerer Gustav. Big Ass Gun.