This enemy is the Alien variant of St. Pigge the 2nd. She has high health but relatively low damage and range. However, she has 100% chance for a Lv. 3 Shockwave, so she will punish the player for spamming meatshields.
Anything that freezes Aliens and is decently bulky such as Surfer Cat, who can rush in without getting knocked back, can immobilize Elizabeth the LVIth, allowing other units to attack her without trouble (e.g. Valkyrie Cat).
If you are fighting Cli-One or Corrupted Valkyrie in Into the Future's Moon stages and Elizabeth spawns, that is a sign that you have taken too long to beat the stage and that everything is about to go horribly wrong. Either retry the stage, or come back later when you're stronger.
In a late-game scenario she is pretty easy to deal with because of the Wave Blocker ability that some cats have in their True Forms. Since she has low damage for a wave attacker, it will be especially hard for her to deal with a stream of Octopus Cats. And if you were lucky enough to receive Cat Machine, its True Form can even defeat Elizabeth in a one-on-one fight.
Other Wave Blockers will come in incredibly useful against her, especially if they're tanky and can protect units behind them. Though they are few in number, units like Mightycat, Eva Unit-00 and Hell Warden Emma can protect units behind them.
Some units have a different ability, called Shockwave Resilient, which protects them and only them from the damage of shockwaves. They are much higher in number and can effectively damage her without taking too much damage.
56th queen of the Pigpen Kingdom. She turned blue after 7 mushrooms got stuck on her throat, causing her to choke. Moves around without permission using a crown she found around. Can release shockwaves.