Name	Lifeboat from Titanic	Lifeboat to Carpathia	Confidence Level
McCarthy, Miss Catherine	15	15	3.00

Miss McCarthy wrote to her father shortly after the sinking (On Board RMS Titanic page  357)
   “I then left the room, and on going out I met a man from Dungarvan, who took me up to the second class boat deck, where they were putting out the boats. I was put into one boat, but was taken out of it again as it was too full. I was in the last boat to leave the ship, and was the second last person put into it. This was a short time before the ship went down. We were only just out of the way when the ship split in two and sank. We remained in the boat all night until near eight o’clock next morning, when we were rescued by the Carpathia. Our boat was so full I thought it would go down every moment, and one of the boats capsized when we were leaving the sinking ship.”

Much of the following uses the logic given by Brian Rose in one of the Facebook groups.  We agree with his logic.
    "Boat #15 is the likely candidate for two reasons, both of which are contained in a letter she wrote to her parents after she was rescued. The first detail is that she describes boarding a boat on the "second class boat deck." This would strongly suggest she entered one of the after lifeboats, which were abaft the second class promenade and entrance. Many third class survivors entered boats in this area by climbing the ladders from the after well deck, and then gaining access to the second class staircase up to the boat deck. This was the most direct route for a third class woman, who were all billeted aft. From where she was located, it would've been far more difficult of a route for her to go to reach the position where Boat D was located, absent some kind of guidance from crew, as was often the case.
    The second detail is that she describes the first boat she sought to enter as being too full, and having to enter another boat as a result. On the starboard aft side the boats were launched in numerical order - first 9, then 11, then 13 and then finally 15. All of which but 9 were heavily loaded. We can eliminate 11, because she would have had no difficulty entering boat 9. She could have entered boat 13 after failing to enter number 11 (as was the case with Ruth Becker) but then how could she have failed to mention that boat's near sinking and collision with boat 15? It makes the most sense that she initially sought to enter boat 13, and instead went to boat 15. For the same reasons as to why we can eliminate boat 9, we can also eliminate boat 4, which would have to be the boat she tried to enter first, if she indeed boarded boat D. But boat 4 was not heavily loaded, and I don't think she would have had difficultly entering this one. That boat 4 carried almost entirely first class women, and was loaded from a first class segregated part of the ship (the 1st class promenade) would go further to persuade that she did not enter a forward boat.
    She does, however, mention about a boat capsizing while being launched. She could be referring to boat B, but I think it more likely she was referring to boat 13, which nearly did capsize. Given how dark it was, this could be a reasonable error on her part, and lend credence to boat 15 being the last boat.
    ET [the website Encyclopedia Titanica] suggests that she might have boarded boat 16. We do not feel this is very likely because the port aft boats were lowered in reverse numerical order. She would have not likely been turned away from boat 16 had she sought entry, and if she had, she would've gone forward to boat 14, or 12, none of which could by any stretch be called the "last boat." And then you have the issue of why she did not note the gunshots being fired by Lowe.
    Which is not say it's impossible that she boarded Collapsible D. She could have also boarded boat #10. But without hard, absolute data, we can only go by weighing the best available evidence, which in this case is that she boarded boat #15."

Though we are not positive of #15, it is by far the most likely.