Adopted a new kitten and then my 7 month old kitten went into her first heat and is acting crazy.

I’m hoping for some advice. I have a 7 month old female cat, she’s been very lonely since her sister passed suddenly back in May. So I thought she’d like a new companion. I committed to adopting a 8 week old male and literally the next night (before I picked up the new kitten) she went into her first heat! We have her scheduled for getting spayed in two weeks so the timing isn’t great as I was hoping she’d be spayed before heat. But she’s acting so weird and unfriendly now that the male kitten is here.
She’s even hissing at and swatting at me. I’m giving her space.
I know introductions take time but I want to ensure they’re both comfortable and safe.
But any advice on what I can do to help this transition?