Many reasons to spay. Cats go into heat repeatedly, every few weeks, until they get pregnant or spayed.
A cat in heat WILL get out, eventually. And once out she WILL get pregnant. Or lost. or Killed.
Spaying prevents uterine cancer and pyometra (infection of the uterus), both very serious and usually fatal.
Spaying greatly reduces the risk of breast cancer. With every heat cycle her risk of breast cancer (and the other two diseases mentioned) increases.
Endless heat cycles are rough on the kitty both physically and emotionally. And misery for everyone else in the house too.
No, her personality will not change, she is who she is.
How long has she been with you? It takes time for a cat to adjust, and for her personality to blossom. Growling at other cats and people is normal for a cat in a new situation.
As for the female being top ranking cat....well I have three girl cats and one male, and HE is Top Cat, they all kowtow to Himself.
PS my kitten was only recently spayed, and her personality is as delightful as it was before the spay.