I was looking at the timing chart and realized that you only ever remove a ship in 10. When using a "perform this attack twice" weapon you only ever hit 10 after the second time you perform the attack. Making the second attack is a mandatory effect.
If Miranda is down a shield but shooting her TLT at a target with one hull then she can make her first attack with all three dice and if she misses the first shot make a second shot with all three dice. If the first shot hits and removes the final hull from her target, she can use her ability to make a two dice attack against the destroyed ship to regain her hull.
Edited by WWHSD