By NO means an expert, but I was and am exactly where you are. Had a 3B that a couple of coaches that thought she should catch and we switched. Here's my take:
Pro's- she should be one of the leaders, never gets bored, grins ear to ear at plays at the plate, enjoys firing back a throw at the pitchers head when she is missing her pitches and making her chase the wrong way (lol), great scholarship opportunities, enjoys the special bond with her pitchers, loves calling own pitches
Con's- hard work without the glory, all of your best friends are pitchers (lessons), every joint in her body pops like knuckles, extra equipment on hot days.
What type of person does it take - does she automatically become the leader
She has to want to make the switch. If there's resistance, don't go there. Most won't automatically assume the leader role and be vocal, that takes work. When you find the right answer, let me know.
Is their a preferred body type - she is tall and slender, will this work against her
Tall is good, but there are all different body types catching at big schools. Like Canocorn said, fast feet & fast hands and top notch knowledge of the game (eventually).
How significant is the injury risk
High. During the game you pretty much just have to deal with plays at the plate (a good coach will teach how to do this properly) and hurt fingers from foul tips and ball bounces. Off the field it's your typical shoulder and knee problems. Many, many catchers have knee surgery eventually, some while still in high school/college. Stretch and ice, ice, ice.
What is a good split time (?) (meaning time from release out of pitcher's hand to pop of glove @2nd base) for a strong bracket catcher at the 12U/14U level and then HS
The terminology you're looking for here is called "pop time" and it is timed from the pop of the catchers glove when the pitch is received to the pop of the glove at 2B. 12U should be in the 2.00-2.30 range, depending on what year of 12U. By 13/14 years old, she should be under 2 seconds. For late high school and recruiting for college, 1.60-1.75 would be ideal, but some will be ok with the 1.8-1.9.
A great catching coach, the desire, and work ethic are crucial. Good luck!