Beth made some very good points. I am happy to have her here helping. I agree that not eating usually isn't a problem. Perhaps in this case a vet visit would be a good idea. A female dog's reproductive cycle is different from humans. Often it is called the heat cycle or season. If she is only a year old, I wouldn't be expecting her second one now. When was her first? Usually it is close to 6 months until the next. So likely you have time to have her spayed now. The problems with her nipples and it is called a vulva could be something else that does need vet care. Or she could be pregnant or infected. Better get her to a vet and find out for sure what is going on. If she is coming into heat, watch her very carefully. There are not enough homes out there for all the Boxer mix puppies. We end up slaughtering unwanted dogs by the millions.
The not eating could be several things, she is sick, some dogs lose appetite when they come in season, or the most common cause is over feeding. Most Labs will devour more that is good for them and look for more. Some dogs refuse to eat more than they need. Check her ribs using the method illustrated in this link,
http://www.puppychow.com/products/po...condition.aspx Have the vet confirm your judgment. Then try to adjust her food and exercise.
Put down the dish with what the dog should eat, and give it 15 minutes to eat. Then take it up. Do not give it anything to eat until its next scheduled meal. In a few days, it should be eating what it needs. Continue to check its ribs and adjust the food as needed. This is not easy. I had a Shepherd go 3 days on a few nibbles. I was a wreck, but she was fine. It is almost unknown for a healthy dog not to eat what it needs. Unfortunately, in too many cases, it is less than the package says, and less than the owner thinks the dog should have. Many dogs are quite good at holding out for tastier chow. Like kids, sometimes it calls for tough love.