The heat cycle lasts a full 3 weeks or a little longer but the mood change and changes to her body will last approximately two months. Your girl could go through all the same feelings and changes that a female that has been bred would go through. This is why so many females experience false pregnancies.
Your main concern should be that as your female gets older she is much more likely to get pyometra (an infection of the uterus). This is why it is highly recommended to spay a female if she is not going to be used for breeding. Pyometra usually can show up a few weeks after the heat cycle ends.
Please read the following article so you will be aware of the signs of pyometra.
Pyometra In Dogs | Causes, Symptoms & Treatment | VetsNow
You best option would be to talk to your vet about when would be the best time to have her spayed. Hopefully she will get back to her old self soon.