I always found it interesting that these little girls, Meritaten-tasherit and Ankhesenpaaten-tasherit, are only seen on the monuments which originally belonged to Kiya. That's why the alternative theory is that the little princess depicted on the monuments is actually the daughter of Kiya (sometimes referred to as Kiya-tasherit

).
That theory says that Meritaten-tasherit is identical to Ankhesenpaaten-tasherit and refers to a daughter of Akhenaten and Kiya.
Who knows?
It is true that Amenhotep III married his daughters Sitamen and Isis. He may have also married Henuttaneb. There's some evidence that suggests that all three are elevated to Great Royal Wife.
Ramses II married his daughters Meryetamun, Bintanath, and Nebettawy (and possibly more). Meryetamun was elevated to great royal wife in ca year 24, possibly to replace her mother Nefertari who is thought to have died around that time. Similarly Bintanath seems to have in some sense replaced her mother Isetnofret. Bintanath is known from her tomb to have had a daughter, indicating that the marriage was nor ceremonial.
The only royal woman I know of who married a non-royal and made a life for herself is Ramses II's sister Tia. She somehow escaped the royal harem. I wonder if she married before her father became king? Other than that the options for royal women, specially princesses seem pretty limited.