Interesting she even mentioned her husband was going to move in at all .. you'd be miles away before all the boxes were unpacked.I'd let her know she needs to have him submit a application, you'll run it, if it doesn't meet your criteria then you have give him written reply, to HIM that he doesn't qualify and to HER her roommate didn't qualify for the add on to the lease.

Just want to add one more: considering prices have been up significantly, I would take a grain of salt on the COMs. 

I had the same question and decided to add one to our Lake Michigan rental.

I look at it as appreciation, a nice add on to look at end of year.