In XPath there are a couple of ways you could try this.
Match by text (can be partial text too)
Match by tag (if that helps isolate the label from other labels)
Match by partial tag value
Note the brackets surrounding the selectors before the index
If you leave these out then you will match the first element of each branch of the DOM which matches your selector, e.g., the following will return the set of the first label element in each branch with a for tag containing the value 'radio-button'. NOT the first matching element from that set!
Looking at the html that was edited out of the question, you probably want one of the last two examples.