I've just found more evidence that Dyrath is the second daughter:
Source:
Dyrath - Warhammer - The Old World - Lexicanum which cites Sigmar's Heirs.
The connection to Haleth, which might be a variation of Halétha, means that she's now my number one guess for the other daughter.
She's a goddess of Womenhood—which fits the yonic symbolism—she has a secretive cult, and the Hägercrybs are forested hills, and both forests and hills fit the chevron symbolism as well.
Assuming Halath and Dyrath are not aspects of Rhea but actual independent deities, then Halath must be Halétha and her sister must be Dyrath.
This is all that Heirs of Sigmar provides on Dyrath, with citations and page numbers:
"Rhya, too, has her sub-cults, such as Haleth in the north and Dyrath in the west, the latter symbolising her aspect as Lady of Fertility and Midwifery" Page 40
"Other popular deities are Dyrath, a regional name for Rhya whom the Reiklanders of Vorbergland honour as the patroness of fertility" Page 81
"Dyrath's spindle": Destiny or fate. (From the belief that the umbilical cord is spun by Dyrath and handed to Morr, so that he may pull people into his realm when it is their time.) (Sayings of Reikland) Page 81
"To the north Rhya is called "Dyrath," a sign of Reiklander influence." Page 96
"Others devote themselves to lesser aspects of the major gods, such as Dyrath in the Reikland and western Sudenland and Averland, who is a local aspect of Rhya and is the patroness of fruit trees." Page 99
There is also a misspelling of her name in Page 42 where she's identified as "Dryath", a Fertility Goddess of the North.
The use of the word "sister aspect" is not present within canonical sources. That's an addition by the Wiki. If you're wondering what Tome of Salvation has on Dyrath, this is it:
"Where the wild-haired priests of the Teutognens put any cultist competing with Ulric to the axe—thus, by the time of Sigmar's birth, there were no cults openly claiming to represent winter, wolves or war—most other cults were less aggressive. Indeed, some cults did not even try to enforce their religious views, which resulted in some Gods being worshipped in many different ways, and by many different names. A good example of this is the many Earth Mother cults that can be found throughout our pious Empire, including the minor cults of Dyrath, Haleth, and Hyacinth, which, amongst scholastic circles, are all presumed to be revering Rhya under different guises." Page 13 ToS
And then there are two tables that list her as a Fertility Goddess in Reikland. (Pages 79 and 81)
If there is demand for it, I can pull up all mentions of Haleth.
