I am going to preface this with the comment that I don't have anything against lefty catchers. I have had them on my teams in the past. But the comment that a lefty has an advantage and is more desired at catcher than a righty, has me intrigued. Why would one be more desirable at catcher than the other? Both have their pros and cons.
Last comment for the OP, catchers, especially at the younger age groups, that can block well are rare. Think about a young pitcher that is usually a little wild. Keeping balls from going to the backstop saves more runs than stopping a runner stealing second. NECC is the gold standard in technique. We teach ours in order of priority the skills of receiving, blocking, pass ball handling, bunt coverage, then throw down.
Protect her throwing hand (thumb inside fist) behind the back or outside the knee, don't turn your head (less protection when turned), watch and wait for the pitch (and forget about the bat), and have fun!