Whereas Hawkgirl was created as an integral part of the Silver-Age HAWKMAN feature, Mera-- DC's first Silver-Age character to marry the hero of her feature-- seems to have come about by happy accident.
Arguably, the template from which she derives is not so much Hawkgirl, Lois Lane or Carol Ferris, but that of Superman's nemesis Mr. Mxyzptlk. Although Mxyzptlk remained a perpetual thorn in the side of the Man of Steel, it might be argued that he indirectly spawned a plethora of helpful imps who either regularly or irregularly assisted DC heroes. 1959's "Bat-Mite" was conceived in the vein of a pest who wanted to be helpful to Batman, but others were better helpmates, like "Cryll," a shape-shifting alien who started assisting Space Ranger regularly in 1958. The first issue of Aquaman's 1962 magazine introduced a helpful extra-dimensional imp, "Quisp," who was only made occasional appearances. Quisp would be phased out of the feature as soon as Mera appeared in issue #11, and not only did she take his position, she was also given, via editorial fiat, the same powers Quisp had displayed: the ability to manipulate water much as Green Lantern manipulated his ring's energy, turning water into solid, offensive objects like clubs, fists, or, as seen above, giant monsters.
Mera quickly became a dominant force in the feature, somewhat shoving Aqualad to one side. She married the titular King of the Seven Seas in issue #18, about a year after her debut, and gave the feature a more domestic feel, particularly when she gave birth to Aquaman's first son.
Mera's popularity, like that of many other Silver Age heroines, has waxed and waned many times. At present, she seems to have undergone a slight rebirth, thanks to the "Brightest Day" series. Not surprisingly, I find that she, like Star Sapphire, had her best stories in the Silver Age and never quite made a meaningfuil transition to the current era of DC Comics, as did characters like Batgirl and Black Canary.