Minnesota Furnace broke - Renter demanding discount

[Nick Johnson]

We recently had a furnace break two weeks ago and the renter is demanding a refund.  The night we were notified, we examined it found some loose connections and got it running again.  The next day it broke again we delivered multiple electric heaters, and scheduled an inspection from an HVAC guy.  long story short it took a week to fix as we had to do an entire replacement of our HVAC system.  When we visited the property the second day it was 70 degrees inside, the HVAC guy assured us over a period of 3 visits through the week that "the house is plenty warm inside".  Outside temps throughout the week were in the low 30's which is unusually warm for Minnesota.

The renter is now demanding a rental reduction, or will take action.  The renter has stated two different low temperatures, neither which were experienced by us, or the HVAC guy.  The renter claims the electric heaters were not adequate as they were blowing circuits.  We told her upon delivery of the portable heaters, and one more time the heaters draw too much power to be on the same circuit and should be spread through the house.

Any advice on our responsibility as a landlord, and how this may play out if we go to small claims court?