Why does my toddler only walk on her tiptoes?

My nephew did this for a while and doctors were concerned that the tendons were maybe too tight (I can't remember which ones) If it had persisted they talked about braces but he grew out of it. I've also heard it could mean some sort of neurological problem or autism but those are worst case scenarios. Walking on tip toes is very typical toddler behavior.
I would talk to your doctor about your concerns. They might be able to give you some exercises to help or say whether or not it is something you even need to worry about.