I have always strongly been against "juvenile" spays, meaning less than 5 months. I recommend shooting for 5 1/2 months. The reasons are: full capability of the bladder sphincter (control valve) is not achieved until some exposure to estrogen which typically occurs around 5 months and I also believe dogs spayed at less than 5 months hold onto more "baby fat" and juvenile body proportions. There is no big rush to remove any remaining temporary teeth so 5 1/2 months is a good time. You can find plenty of info recommending juvenile spays, much of which is generated by groups seeking to curb the puppy population explosion and also some from legitimate medical sources but I believe 5-6 months is s good time. You do not want to let her come into heat for both preventive medical reasons related to breast tumors and also for convenience.