Every franchise has its own fanbase. And where there's a fanbase, there's shipping.
"Shipping" is a term used to describe characters being paired together in a romantic relationship. Often times, there will be a name given to these ships, typically the combination of both characters' names, such as "Stucky" referring to the characters of Steve Rogers and Bucky Barnes from the Captain America franchise.
Another popular ship within the MCU community has been Valcarol, which is the ship name for the characters Carol Danvers and Valkyrie. One such fan in support of this ship managed to notice it possibly being referenced in the latest Ms. Marvel sizzle reel, with the young superhero fan, Kamala Khan, being a supporter of the pair.
Twitter user @velmcrite noticed a very interesting piece of apparel worn by Kamala Khan in the sizzle reel for Ms. Marvel released at Disney's Investor Day, which shows Carol Danvers' Captain Marvel (left) and Valkyrie (right) standing side-by-side.
WHAT THIS MEANS
While it is fun to think about Kamala Khan potentially being such an obsessive Avengers and Captain Marvel fan that she would be shipping her with other heroes, there's a possibility that this shirt could be more of a reference to A-Force and that at least one other female hero is being obscured on the left of Carol.
On the other hand, Marvel Studios is likely aware of this ship, as even Brie Larson took notice of the fan concept when it began to grow in popularity within the community, tweeting out fanart of the two characters saying that she'll "never stop loving this ship."
Additionally, in the comics, Kamala Khan once teamed up with Spider-Man and told him that she always shipped him and Carol, even referring to them as "Spider-Marvel."
So, it wouldn't be a stretch to think that Kamala will do the same in the MCU. As for how or why Valkyrie is on the shirt, keep in mind that this is after the five-year time skip and that she had been essentially the king of New Asgard for that half-decade while Thor sulked.