We have a tenant that has requested that we install a temporary ramp because her son is having leg surgery and won't be able to walk for a month. Is this something that we are responsible to pay for? I thought of asking her if her insurance would cover any or all of it...what do you think?

That is absolutely not your responsibility. I would allow it only if it was done by my licensed contractor and she paid for it.

I had knee surgery in 2006 when i was in the Marine Corps -- i lived on the 3rd deck and someone would have laughed me out of the building if I had requested a ramp.

I would agree to allow her to install one at her own expense, not mine, under the condition that she sign a statement agreeing that she remove it and bring the condition back to normal at her own expense within x days (maybe 60 if he needs it for 30).  It is my understanding even if it were covered under the disability laws that you would not be responsible for providing it, just that you allow the modification if it is not burdensome and that they must return it to normal when no longer needed.  

thanks for the responses, I appreciate them.