That is so normal. Hervulva will swell and get redder during her season, especially in the middle of her season. The reason for this is the vulval shape changes, ready for mating. A female dog is only ready to mate for a few days in the middle of her season. Licking herself is normal too.
How long does a menstrual cycle usually last?
Usually 3 weeks, or about 21 days, but the beginning of it can be missed if you don't notice any obvious blood-spots anywhere. A good sign that it's starting is your dog will probably start to lick herself a bit more than usual. The sexually active phase usually lasts for about 5 days (can be a week) right in the middle. Be careful here! She will be inclined to mate with any male dog she comes across! Even neutered male dogs can be sexually active sometimes (but of course there's no concern about her getting pregnant there!) If you intend to breed her to a chosen mate and do not want her to breed with any other dog, you will have to keep a very sharp eye on her
With dogs, although it seems like a 'menstrual cycle' it is very different to humans. In fact it is ovulation in dogs.
As ginger stated, the heat cycle lasts for about 21 days. Her vulva will be VERY swollen and she will spot red blood for about the first week. After that, the spotting will stop, but don't relax, because after she stops spotting is when she is most likely to allow a male dog to breed her. Don't consider her to be out of heat until all the swelling is gone from her vulva, because even if it's longer than 21 days, if she is still swollen, she can still be bred and she can still conceive. So don't think that just because it's day 22 that nothing can happen.
Is there a reason that you have not had her spayed? Spaying a dog before their first heat cycle almost completely removes the chance of her ever developing mammary cancer as she ages, and no matter how old she is when she is spayed, once her uterus is removed, you will no longer have to worry about her developing pyometra, which is a life threatening infection of the uterus, and very common in unspayed females. If you were to have her spayed as soon as this heat cycle is over, she will still have a GREATLY reduced chance of developing mammary cancer, so it's definitely something to consider if you are not going to show and breed her.
Ghilly