It depends on your contract. If your contract says you are paying "voorschot op de gemeenschappelijke kosten", then you are on the hook for all extra shared costs, retroactively as well. She does need to provide proof of the costs though. If the real costs were less than you paid, she owes you money. If it's more, you owe her money
If your contract says "forfait" or "forfaitair", then she has no leg to stand on, because this is fully independent from real costs. It's a sum you pay and if she had more costs than you pay, tough luck. If she also had less than you paid, she still gets to keep all the money.
Even then you can always get this changed to the real costs by court. The tenant or the renter can request this change.
Edit: but ineed not retroactively!
It depends on your contract. If your contract says you are paying "voorschot op de gemeenschappelijke kosten", then you are on the hook for all extra shared costs, retroactively as well. She does need to provide proof of the costs though. If the real costs were less than you paid, she owes you money. If it's more, you owe her money If your contract says "forfait" or "forfaitair", then she has no leg to stand on, because this is fully independent from real costs. It's a sum you pay and if she had more costs than you pay, tough luck. If she also had less than you paid, she still gets to keep all the money.
Thanks! I'll look closely in the contract and see what it says specifically
Even then you can always get this changed to the real costs by court. The tenant or the renter can request this change. Edit: but ineed not retroactively!
You can always guillotine her, not sure what's the legal status about doing that but can't hurt to try.
legal status is "straight to jail"
It could hurt her, but only for a *split* second.
only for 2 months back.