So, I have been making my own pantheon for a setting by ‘rolling’ on the gods section of the “Motif-Index of Folk-Literature” and what I got for a chief deity was: Mother of the Gods, Supreme God, Culture Hero as Trickster, and God of Dawn. So far I have come up with the idea that the goddess overthrew a previously tyrannical sky/night god either by using trickery to kill them or imprison them and taking over the position as supreme god of the pantheon. Do you have any other ideas that I could use to flesh the goddess out?
So usually when you have a "usurpation of the pantheon" type event in mythology, its a parallel to a cultural/ethnic shift in the region with the old gods being the patrons of that previous culture. Greek mythology is actually a great example of this as there's an initial creation story ( primal chaos gives birth to the earth and sky) then an initial pantheon ( the titans who were birthed from earth and sky) and then a secondary pantheon (the Olympians) who overthrow the titans, who are either killed, imprisoned, or married into the existing pantheon, you then have the emerging pantheon of greek cultural heroes, who if they stuck around long enough before Rome/Christendom took over might've ended up getting deified themselves and overthrowing the Olympians.
The combination of elements you've gotten is very interesting, but actually presents us with an interesting character arc as you've already hit upon. Rather than the night sky (which still happens every night) I'd say that this goddess overthrew a deity of harsh and terrible winter, an event that just so happened to coincide with the end of an ice age.
Here's how I'd set it up: The "Ethnic" god of these lands was a river god, bringing fertility, bounty, life, all that fun stuff. This god had a sibling (younger or older it doesn't matter) who felt snubbed for the position of chief god/unloved, and so brought down an endless winter upon the land, freezing their brother and usurping his place as king. The winter lasted so long that the fields dried up, the animals died, and the offerings stopped, and so and this usurper turned to devouring people (and perhaps other gods) in his hunger for worship and flesh, reigning over a half forgotten dark age.
In comes our trickster, who's family have been one by one eaten by the mad god of winter, until it's just her and (insert sainted family member here). Red-mawed winter comes to devour that person and our trickster says "I bet I can find something more glorious for you to eat, so if I go and get it for you to eat instead, will you spare my family?" "That sounds great" says Red-mawed winter, " But I'm hungry now, so you have to get back to my temple on the riverside by ( insert possible deadline)" Commence heroic quest into the east with unlikely supernatural aid, eventually culminating in trickster getting the sun and placing it in (seemingly innocuous container that will become part of the iconography of the religion, chest, urn, amphora etc) before carrying it back to the palace of Red-mawed winter in the west ( which just so happens to mime the sun's passage across the heavens, and line up with the origin of this river). Red mawed winter is greedy to have this bright and shining prize, but upon taking it out of the vessel, the sun unleashes summer in it's fullest force, melting the ice, freeing the rivergod, and turning red-mawed winter into a pile of bones and bloody slush.
Trickster ends up Marrying the Rivergod (who cedes her authority over the land as she saved his life) and having lots of kids to repopulate the ranks of the devoured pantheon, the bones of Red-mawed winter are imprisoned in a deep vault/scattered across the earth/whatever you need for them to be evil relics later in the campaign. Trickster now rules as the Summer queen, with day being when she presides over the land and night being when she goes back to visit her husband.