Hello and welcome to MedHelp's forums. We're glad you are here and have asked this question. I'm sure this is concerning. Here is some general information that may be helpful https://www.webmd.com/children/central-precocious-puberty#1. The good news is that you have seen a pediatric endocrinologist and they did not find at that time to be anything abnormal and things do not sound like they have changed for your daughter. Is she showing any other signs of puberty from the list in the article? Another important thing to point out is that the sign that your daughter is having is much less concerning for girls than boys. That's hopefully a little reassuring for you. However, I do see your point. Your pediatrician may be able to do the blood work to check her hormone levels for reassurance. Is she growing at a normal rate?
I've learned more and more about precocious puberty over the years. I have two nieces with it that did shots to prolong menstruation. Both were very small in stature. One grew to 5 feet 8 and the other is 5 feet 4. That wasn't the main concern although being smaller than everyone else takes an emotional toll on kids even girls, but lack of growth hormone can impact other things like fertility, etc.
If it were me, I'd hold off for a while and then get her tested again. I'd wait a couple of years and then do it for peace of mind. If your insurance covers it now, then what is the harm. I believe thy examine, do blood work and then x rays of bones to determine. The x rays may be the expensive part. Or perhaps the lab work. But if it is financially feasible for you, why not know? If you are just going to question though in a few years, then wait.
I did read that it is less of a concern for females than males to have early pubic hair. Although 15 months!
Your little one is probably getting ready for kindergarten. Crazy to be talking about puberty, isn't it?