Catcher begins to throw to thirdbase but does not throw due to CR in her line of fire.
This is from the OP. The scenario offered specifically states that the catcher "begins to throw" to 3B.
There is absolutely no doubt in my mind this is interference based on the information offered. No mind reading, second-guessing, reading into the play, etc.
If you choose not to call INT due to "no throw, no INT", what are you going to do when the catcher clocks the CR-to-be in the ear-hole?
"But Blue, you told me I had to throw the ball!"