The element in our electric oven has been sparking lately. could it be caused by our oven thermometer?

I think you are reading the situation correctly and proving the obvious irresponsibility of your land lady. You at least need a new element which is easy to replace if you have the model #. I've never seen one spark they usually just go out at one area and eventually die. The sparking would make me tend not to use it until you get it checked out.