There are actually several ways a Queen can be made that aren't completely ridiculous (to me, anyway):
- A lone Drone can force a host to morph into an egg. This can egg can house either a normal facehugger or a Super Facehugger. The latter carries at least two embryos, one of which is a guard (a normal Drone/Warrior or, technically, a Praetorian), the other being a Queen. That's what's been established in the films. (A Queen can also probably lay such an egg if it feels its time is coming to an end.)
- After being exposed to an uncertain amount of Queen jelly (whether or not being exposed to Queen jelly is actually vital to the transformation process is debatable), a lone Xenomorph goes through a lengthy process of morphing into a Queen. This usually happens after the previous Queen dies or the current hive is overpopulated. If overpopulation is the issue, then, if the Xenomorph is successful in morphing into a new Queen, a rival hive is born, and the two Queens battle over supremacy, the victor becoming the planet's resident Empress. The Queen that loses may not necessarily die.
- The 'alpha' Praetorian or alpha male takes the place of a Queen that has recently died. A Praetorian becoming a Queen would be no different from a Drone/Warrior becoming one, though whether or not Queen jelly is a factor at all is questionable, since they're already a "pure" strain.
What I've listed certainly may not be all there is, but of everything that I've ever read, I feel those can coexist very comfortably in the life-cycle canon. Technically, yes, a Praetorian
is a royal guard, but it's always been my belief that a Praetorian is simply an immature Queen, like a 20-year-old college student compared to her 46-year-old mom. One pair consists of a salivating, rough-skinned bitch producing a convoy of eggs through her fat sack while her child can do nothing but wait to become her, and the other pair is from space.