I feel like she should've used the Flak 88. With that cannon, it doesn't matter if the target is grounded or flying, as long as it's big enough.
If she can create effective explosive rockets, nebelwelfer emplacements might be more effective due to their large volume of rocket fire at the start of a battle compared to the sustained fire of cannons. (Katyushas would probably require the truck, and engines are very complex)