Marvin Elevate Replacement Sash Lift

Martin Elevate Replacement Sash Lift

My window installer does not think it may fit; we thought this was a option for these windows (we had two of the 'Elevate' windows installed). One window works (goes up and down effortlessly) fine, the other is impossible for my wife to operate, very tight and she is unable to lift, pull or lock the window. Also, why is this called a 'Replacement' lift? There was nothing to replace on the window, it came without any lift hardware. We are waiting for Marvin to offer a solution. This is also a security issue as if I am not around, my wife can't lock it.