I think you know your child better than anyone first off! secondly, my kids took a late cat nap (making it 3 a day) for a while when they were little). I wouldn't force her to sleep, but if she is cranky, she may need "me" time, just some time alone, without all the stimulation. If she falls asleep, then I'd assume she needed the sleep as well. Is she sleeping well at night? If not, maybe she needs less during the day, but if all is going smoothly, simply say to your advice givers "thanks for your input, I'll think about that" because again, you know best!
Have you heard of babycenter.com? It's a great website. According to them, your baby needs about 14 hours sleep total at 9 months. Typically, 11 hours at night and 3 hours during the day in 2 naps, but again, every baby is different.