I can't imagine what the black spots might be. Is she/he an outdoor cat? Maybe it got into something outside and has been trying to clean the fur therefore upsetting the stomach by licking off the black goo. It is good that your sister is taking Precious to the vets anyway. Lethargy, weakness and wheezing are worth getting a doctors opinion on. Please let us know the outcome of the visit is. I hope it isn't anything serious.