omg are you looking at me in my house RIGHT now!! this is my identical problem. FORMER problem!!
same thing here, pt girl, 15 mos. naps maybe an hr then screams. she used to sleep with another LO in the same room until she started doing this. now i put a playpen in our computeroom in the basement. shut the door, go upstairs. (on main floor) now everybody else can sleep. i can still hear her, but for sure not as loud!! She is safe and eventually settles down. this is a mandatory nap period and her parents are aware of this nap time. it is not fair to me or the others just because she wants to have short naps. The child is better off being left alone to sleep, and only sleep because it is only a couple hours and she needs it. she will eventually learn that at your house, sleep time is not optional.
Good Luck!