Rabbits regulate their temperature through their ears. If things get a bit chilly, a bunny's ears will be colder as they restrict the veins in their ears. When they are hot, the veins in their ears get a bit larger (layman term here), allowing more blood flow there so that they can cool their blood via their ears. Cold ears are not normally a concern UNLESS you see other signs of illness -- not pooping, not eating, or lethargic, etc.
So if your bunny is acting healthy and normal, and the only thing that really has changed is that things are bit chillier than normal, then her cold ears may just be her way of preserving heat. Just make sure she has some cozy blankets and a hidey box to help her stay warm if she wants to. But it looks like if she's doing eating and doing binkies, then she's not bothered much by the cooler temps.