Lol, I’m a bit worried.
She carries her toy mouse like a gift, but the colder weather means the real mice try to get inside.

Well wouldn't you rather she bring you gifts rather than having a mouse roam around the house? lol
She must be practicing for the winter. :)

She’s a bad ass, I would hope she wouldn’t just play with the thing though, lol 😸

I'm sure she is. 😸
Does she play with the toy mouse, or does she just carry it around?

I believe you are correct about her placing it where I would see it!
When she presents her toy mouse, she howls a deep meow sound and does that several times as she comes up the steps. She walks into the room, head held high, then drops the mouse on the floor. She also plays with her toy mice. She will chase and clobber if you throw it, but will also play on her own 😻

See she's practicing for the real thing. 😺
it's also very cute how she plays with them. Mine is sort of the same with bottlecaps, except when he's playing with them, that's an indication for me to come play and scoot them on the floor, like right now. :)