iPhone connects to iMac unintentionally

Hello - I'm hoping someone can help me? I've noticed lately that my trackpad on my iMac is EXTREMELY erratic at times. I've found that a lot of times when this happens, I look under bluetooth devices that are connected to my iMac and my daughter's iPhone is connected. I disconnect her iPhone and it seems to help - the cursor on my trackpad goes back to normal movement for the most part. What I don't understand is: why is her phone connected via bluetooth to the iMac? We have 4 iPhones in the house, and hers is the only one. Two, she doesn't even know how to connect her phone to the Mac via bluetooth. Three, her list of devices in her phone doesn't even include the Mac. And three, when I manually and intentionally tried to connect her phone via bluetooth to the Mac, it gave me a code to put in, which I didn't do. And also, I disconnect the phone in bluetooth on the Mac, but when I get back on the Mac, it's connected again.

I'm wondering how to stop her phone from connecting to the Mac, and also if perhaps I'm being hacked and the connection is disguised as her phone? This is really strange . . .