I went all winter without furnace heat in central Indiana.
Never dropped below 45 but I was using a woodstove to get thru overnight and whenever I was there to tend to it.
2 options:
Get a 110v light timer to cycle the window unit(s) [might also work with space heater esp. if you could confine your dog to the warmest best-insulated room]. Maybe there’s an option for a 220v timer too?
If you have an electric clothes dryer disconnect the vent hose and clean all the screens and hose airways. Put some old panty hose over the end of the hose or secure with used dryer sheets. You may only be able to run the dryer for an hour or so with heat on high, but I was able to get an extra 5 degrees/hour - downside is you spend a lot more time dusting everything.
Be careful with the timer - it’s a good idea but a light timer doesn’t have the contact rating for a heater... just look at the ratings.
Ya got three units run one .... and crack the window open.