Is my kitty okay?

My cat is thirteen, almost fourteen. She has had a lump on her neck for a while now, but she hadn’t shown any symptoms of it bothering her until recently, so we let it be. Lately, she’s been keeping to herself more than usual (she really only likes my mom, anyway) losing weight, and her fur seems like it’s not as smooth as usual. Today, I found her upstairs sleeping on a bag. She kind of groaned a little bit, but she started purring and letting me pet her. She even let me carry her downstairs (she never lets ANYONE carry her, not even my mom) her breathing seems a bit labored, but otherwise she’s seems to be okay. She walks a little slow, but she’s still eating. She won’t play with our other cat very much anymore, either. Should we be preparing for the worst? (We are taking her to the vet as soon as we can to have her checked out.)