Has anyone tested positive for COVID for more than 10 days?

It's my niece's first birthday party tomorrow. I started with feeling lousy on September 28th. Ended up doing a rapid on the 30th. I got a whole bunch of tests and have been testing every day since. I have no symptoms and I've had no symptoms now since the 8th. The line has gotten fainter, but I can still see it.

My sister says I'm just shedding dead virus, and I'm no longer contagious. I said I'm still positive for COVID though. She says the test doesn't pick up whether you're contagious or not, just if the virus is there. I don't get it. If the virus is there, you're contagious! I always heard that you're contagious for five days from the day you get a positive, so I am still contagious then!

She said it's up to me if I want to come to the party or not, but I don't know how long I'll test positive for. I work from home so I haven't missed any work. My husband and kids had it before me but they all tested negative like two or three days after they got it.

So how long will I be contagious for and when will I start testing negative?!