My friend has a son who is very much like this.
He is completely normal in most other aspects, he's around 13 months now, and up until he was about 10 months old, he couldn't crawl, he could sit well, and roll and things, but he would NOT weight bare on his legs, you'd try stand him up, and he'd just flop his legs, and he is also quite a "floppy" baby ITMS? Like my DD is quite solid when you hold her, but her DS, just seems reeeeaallly relaxed lol.
But anyway, he crawled at 10ish months, of his own accord, one day he decided to get up on his hands and knees (no prompting), and literally the next day he was crawling! Out of the blue! He is even standing himself up and cruising along furniture now, again, of his own accord, and in his own time
Does DDs siblings tend to bring her the things she wants? Perhaps that could be a facor, she knows they'll get it for her?

If something in your gut tells you something is wrong - its better to be safe than sorry IMO, but if she seems to be fine in other aspects, maybe leave it awhile longer and see what happens?

Hope I've helped


Sent from the mobile world of iPhones - while no doubt i should be elsewhere!