My yellow female lab is 13 months old and she weighs 90 lbs. I feed her 4 cups of food a day but she does like her treats. Is her weight normal?

Proper feeding depends on several factors including: physical size (how tall she is at the withers; how broad her chest is; how long she is; etc.); how active she is; the type and quality of the food; etc.

Has she had her yearly vet check? If so, what did the vet say about her weight?

90 pounds sounds overweight for standard size labradors of any age or sex. Is she purebred? Labs are notorious for becoming overweight extremely easily.

What type of food are you feeding her and what type of treats?

One thing to remember is that you should cut back her food to account for her treats. My dobie loves getting her food as treats with occassionally another type like liver treats. She actually prefers to work for her food even when her bowl is freshly filled.