I'm sure that if Momo was cold, she would move away from the window. She is probably quite comfortablewhere she is sleeping.
And she also has a fur coat on too.
Cats are pretty picky about their own comfort, and would probably try their best, to move themselves to a comfy spot.
I can understand your concern though. I think that cats will get used to whatever tempature is comfortable for you in the house.
Often times Sammy and Romeo will be laying right in the hot sun in front of the window, taking a nap. I will think that they are crazy, because I think it's very warm in that spot, but at that particular nap session, I guess they want to be warm. (afternoon temp here is about 90 degrees, with insane humidity!)
Other times, they will lay in the shower, where the tile is cool, I suppose, and take a nap in there.