Manage gmail label on iPad
In native mail app, under the "mailboxes" left pane, should be two lists. Top one is "inboxes" and bottom is "accounts". Select gmail account you wish to edit in the "accounts" list (bottom). 

You should now see a list of "mailboxes" (apple's wording) which are the same as your gmail labels. Tap "edit" in top right of that pane and tap " new mailbox" on bottom. 

You can now type in the name of label you want to create. If you want nested labels, drill into mailboxes below. 

This should do the trick.