You are in for a doozy

The first bit of evidence (and ironically, counter-evidence) is in Greenpath. We know that Void creatures leak Void at low health, this can be seen when the Knight has one mask or when defeating The Collector. However, after defeating Hornet both times or not, Hornet does not leak Void particles like the Knight or The Collector. Although, many people say Hornet is Void solely because of her black limbs, people will say The Hunter is Void because of this too. Counter-counter-evidence can be given by Midwife and The White Lady. After obtaining the King’s Brand – a mark that Hornet guards so that it is only taken by those who are worthy – Midwife will say “Then you’ve met her perhaps? Her who’d guard the mark, the Gendered Child” because she knows you have the King’s Brand. The Gendered Child. Gendered. This proves that Hornet has a gender, something that Void creatures lack. The White Lady says “It faced the Gendered Child? She’s a fierce foe, strong in mind and body”. Her dialogue proves Hornet’s gender twice. Again, Hornet bears what Void creatures don’t. Hornet was not fused with Void, if she was, she’d lack gender, voice, and a mind. But she doesn’t. Even Silksong’s Steam page proves Hornet’s gender, referring to her as a “princess-protector”. Hornet herself says she isn’t Void in the Temple of The Black Egg and The Abyss

Need I say anything else? Too bad, I will anyway.

After turning on the lighthouse and returning from The Abyss, she can be seen at the very entrance of it. She says “though our strength is born of similar source, that part of you, that crucial emptiness, I do not share”. Hornet literally says “you’re Void but I’m not”.