Is it a sudden recent weight change? If so, hightail it to the vets ASAP, especially if there's any growths, lumps, etc or behavioral/activity changes.
If not, then perhaps not. Maybe just monitoring her diet - don't leave out the crunchy food all day, feed lighter food according to package directions (you'd be surprised if you read the package directions, how much they should eat) and plenty of water.
It could also be their build. I have a big solid black cat that's always been pretty "dense" in terms of his build - he's been as high as 16.5 pounds which was a bit high, and we cut back his food (both the man and I were feeding him, alas) - he was always ok at 14-15 pounds as per the vet, and I'd seen cats of his build go waaay higher than that, weight wise. Now he's older, and hovers at 12-13 lbs.