Given As Payment At A Grocery Store, My Sister Has A Very Worn Out Silver Quarter--the Date Is Worn Off Completely But I Believe It Is A Standing Liberty Coin-anyone Know What It's Worth?

Wondering how much her quarter is worth when there is no date and I can't even find a site where they show the quarters so that we can compare them to see what years the quarter was actually produced! You can barely see the Trust in the 'In God We Trust' part! Looks very old and probably worth something more than a quarter--she was offered $10 dollars for it but refused until she finds something out!