PG&E bill & neighbor - Long rant

So I live in a 100 year old house in a small town near San Francisco California. I live in a 4 bedroom, 2 bathroom home. Only me and my husband occupy it only. It's turning winter soon and is really cold so we take the tv from the living room and put it in the bedroom during fall to winter (spring-summer is in living room downstairs because it's cooler) so we won't use the heater so much. Lately, the mornings in the kitchen you can see your breath and have to put a jacket. It's only maybe 55-65 but living in California I only feel sun and fog, but never in my kitchen! 
So today I got my PG&E bill, it's usually around $245 , this is for my home (maybe 3,000 square feet -/+ ) plus the cottage in the garden (maybe 700 square feet). But the bill for October was $600! Last December the bill was $800 but we did use the heater a bit,so ok . 
But we literally have not touched the heater at all yet, and it's only getting colder. The occupant in the cottage leaves her heater on 24/7, even when she's gone for a week. It's Sunday night now and she left Friday afternoon and her heater is on ! We turner off her breaker, but it's still on ! And the glass window is hot !After I texted her to please be considerate about the bill since we pay it . (we're both leasing, but her bills are included as she was here before us) Since so, we get a $250 discount on rent, cool right ? Not really . $250 is to cover PG&E, water, and garbage. Garbage is $90 every 3 months, water is $120+/- and there's no way she's using $40 of gas & electricity ! Maybe $350 ! 
As we renewed our lease, we told the landlord, but he said he couldn't do anything because it's in her lease, but he could lower our rent in these months by $500 to cover what she used ! But since it is already starting I told him I wasn't happy to be paying all the bill to not use ours at all, and hers when she's not even here! He says he will install a counter for her and we pay separately 😇 . She stays in for about 3 weeks and says it has to be 70 for a condition she has, but throughout knowing her she's proven to be a compulsive liar. Can she not wear a sweater or a blanket in any case ? 
What to do if he doesn't? It's been a week.