Description of dwarf-women:
The Naugrim have beards from the beginning of their lives, male and female alike. They are in voice and appearance, and in garb if they must go on a journey, so like to the dwarf Men that the eyes and ears of other peoples cannot tell them apart. Their womenkind cannot indeed be discerned by those of other race, be it in feature or in gait or in voice, nor in any wise save this: that they go not to war, and seldom save at direst need issue from their deep bowers and halls. [HOME XI: Of Dwarves]
They seldom walk abroad except at great need. Their resemblance to male dwarves has given rise to the foolish opinion among Men that there are no dwarf-women, and that the Dwarves 'grow out of stone'. [LOTR: Appentices]
Why do they look like the male dwarves?
It is said that to each Dwarf Ilúvatar added a mate of female kind, yet because he would not amend the work of Aulë, and Aulë had yet made only things of male form, therefore the women of the Dwarves resemble their men more than all other speaking races. [HOME XI: Of Dwarves]
Scarcity – Marriage:
It is said that the dwarf-women are few, and that save their kings and chieftains few Dwarves ever wed; wherefore their race multiplied slowly, and now is dwindling. [HOME XI: Of Dwarves]
Gimli said they were no more than a third of the whole people.It is because of the fewness of women among them that the kind of the Dwarves increases slowly, and is in peril when they have no secure dwellings. For Dwarves take only one wife or husband each in their lives, and are jealous, as in all matters of their rights. The number of dwarf-men that marry is actually less than one-third. For not all the women take husbands: some desire none; some desire one that they cannot get, and so will have no other. As for the men, very many also do not desire marriage, being engrossed in their crafts. [LOTR: Appentices]
Also they are never forced to wed against their will (which would of course be impossible).
They join their husbands' families. But if a son is seen to be 110 or so years younger than his father, this usually indicates an elder daughter. The sentiment of affection for sister's children was strong among all peoples of the Third Age, but less so among Dwarves than Men or Elves among whom it was strongest. [HOME XII]
The only known dwarf-woman:
They are seldom named in genealogies. Dís was the daughter of Thráin II. She is the only dwarf-woman named in these histories. She is named simply because of the gallant death of her sons Fili and Kili in defence of Thorin II. [HOME XII]