I would do some reading and figure out what works for you and your dog.
IMO I would never spay/neuter unless medically necessary, HOWEVER, I have done the reading and have my house set up to accommodate multiple intact animals, with the least amount of risk possible of an unplanned litter.
If you would like to keep your girl intact until she reaches full maturity (average 2-3 years), you will need to be prepared to deal with heats and the limits that brings (especially for off leash exercise). As well as a huge thing to look out for is Pyometra (infection in the uterus).
For most companion owners, they either don't want to deal with any heats or maybe just one heat. If you are in the first camp, spay before 9 months, usually anytime after the adult teeth have all come in. If you would like your dog to go through one heat, then just 6-8 weeks after the first heat.
I do agree with you though that I would not be comfortable sterilizing a 4 mont old dog.
Do your research and pick whats best for YOU. There are many opinions and research on the pros and cons of each decision. What works for one, may not work for another. So even though you get lots of food for thought on here (Which I think is amazing!) make sure in the end the choice is one that you are comfortable with and can live with.