Some of these are probably a bit more obvious than you wanted, but here are some suggestions:
[name_f]Glenna[/name_f] and [name_f]Glenda[/name_f] are connected to the word [name_u]Glen[/name_u].
[name_u]Ainsley[/name_u] means “Meadow”
[name_u]Hadley[/name_u] means “Heather Field”
[name_f]Petra[/name_f] is taken from the masculine name [name_m]Peter[/name_m], which in turn is derived from the Greek word [name_m]Petros[/name_m], which means “Stone/Rock”
[name_u]Sierra[/name_u], after the mountains.
[name_f]Tula[/name_f] or [name_f]Toula[/name_f] can mean “Mountain Peak”
[name_f]Sana[/name_f] also means “Mountain Peak”
[name_f]Chantal[/name_f] can mean “Stone/Boulder”
[name_u]Nuri[/name_u] mean [name_u]Light[/name_u], which is not quite fire, but maybe?
[name_f]Alena[/name_f], [name_f]Elaine[/name_f], [name_f]Elena[/name_f], [name_f]Lena[/name_f], and several other variants are forms of [name_f]Helena[/name_f], which is a form of [name_f]Helen[/name_f], which might possibly mean torch, if you are going for really tenuous.
[name_f]Bridget[/name_f] was the Irish goddess of fire.
[name_f]Candelaria[/name_f] or [name_f]Candela[/name_f] are derived from Candle.
[name_f]Iskra[/name_f] is derived from the [name_u]South[/name_u] Slavic word that means “Spark”
[name_f]Seraphina[/name_f] is derived from the biblical seraphim, which means “Fiery Ones” and are a type of [name_u]Angel[/name_u].
[name_f]Hestia[/name_f] was the Greek goddess of the hearth and means “Hearth/Fireside”
[name_f]Vesta[/name_f] is basically the same as [name_f]Hestia[/name_f], only [name_m]Roman[/name_m].
[name_f]Aelia[/name_f] is derived from the masculine Aelius, which is possibly derived from the Greek word meaning “Sun”
[name_f]Sunniva[/name_f] means roughly “Gift of the Sun” which would be cool! Plus the possible nickname [name_u]Sunny[/name_u].
[name_f]Tesni[/name_f] is a Welsh name, meaning “Warmth from the Sun”
And it probably wouldn’t work for the character, but while researching this, I came across someone comparing [name_f]Marisol[/name_f] to the Spanish phrase “Mar y sol,” meaning “Sea and Sun.” There is no etymological connection, but I thought that was cool, considering the twins might represent Water and [name_u]Fire[/name_u]!
Good luck naming!