This is a very interesting question, and it is wonderful that you are wanting to know what is best for your little darling.
Female dogs that are not de-sexed do have an increased risk of mammary cancers (breast cancer). The more heat cycles they have, the greater the risk becomes. De-sexing her, even after having 5 heats, may still reduce her risk of developing mammary cancer in the future.
Another very common problem with female dogs that have not been de-sexed, is that they are at a significant risk of developing pyometra, which is an infection in the uterus. This is often very serious and can be potentially life threatening. This risk is much greater in female dogs that have not produced a litter of puppies. The recommended treatment for pyometra involves an ovariohysterectomy.
I would recommend getting your little sweet heart de-sexed as soon as practical to minimise these risks, particularly if she is not being used for breeding. You may feel a bit apprehensive about the procedure, but in the long run it may be the best for her health. Definitely have a further chat to your vet about all of your concerns, so that they can put you at ease and answer all of your questions.
I hope this has helped answer your question. Please don’t hesitate to ask further questions if there is any confusion.