The Queen Mother is the supreme ruler of the entire Xenomorph species; even the Queen Xenomorphs are subordinates to her. Queen Mothers exclusively inhabit the Xenomorph's homeworld. Queen Mothers are protected by the Elite Guards.
Queen Mothers resembled the Queens in a variety of ways, but are different in two obvious places: their size, and their crests which are shorter than a Queen's Crest.
The Mother's nests consist of six orbs arranged around a central orb in which they reside. These orbs contain the prized Royal Jelly which possibly molts a female Warrior into a new Queen or Queen Mother when one is absent, as seen with Specimen 6. Queen Mothers have acute telepathic and empathic abilities which means they can contact their hive over vast distances. The Queen Mothers are similar to Queens because of their ability to lay Eggs. They have been observed waging war on each other, further proof of their sentience.
The Queen Mother has outstanding/horrifying capabilities that other Xenomorphs lack, ones that haven't been witnessed so far by humans. She has extraordinarily powerful telepathic capabilities that allow her to command the whole of the Xenomorph species throughout the universe, and at the same time she can telepathically control creatures that are not Xenomorphs. The Queen Mother, during the Earth Wars, took control of a lot of the human population, turning them into something similar to a mindless zombie. She was even able to control humans that were in such bad physical state that they would be considered dead.
The Queen Mother has also been shown to be able to communicate through dreams/nightmares with other creatures, and has some form of empathic capability. With this, the Queen Mother has the potential to drive people mad.
It is not known if she is the cause, or if the rest of the Xenomorphs have minor empathic capabilities, but before a Xenomorph Invasion there have been more than a handful of cases where people had nightmares about Xenomorphs before even knowing what they are, or that they even existed.
Another strange ability the Queen Mother has is the ability to merge with the Hive Resin. Unlike the Warriors and other Xenomorphs that hide on or within indentations of the Hive, the Queen Mother can use it like it is a portal or interact with it in such a way that it doesn't act as a physical obstruction to her.