Boiling Chicken Breast (or any meat) before cooking to cook evenly
Short answer - you are right on all counts and she's wrong. Tell her that, she'll love it. ;) 

The longer answer is that boiling a frozen piece of meat, especially one that is thick in the middle  like chicken breast is exactly the opposite of what you want to do as you'll cook the outside but the inside will still be frozen, and boiling (as you rightly point out) will remove flavor from what is already IMO flavorless to begin with. Any cooking method will dry the chicken out whether boiling, baking, or frying, so by cooking twice you are liable to end up with food that is overcooked on the outside and undercooked on the inside. 

Cooking frozen chicken isn't a great idea from a safety and quality perspective but it can be done if the meat is cut thin, so your point about butterflying it is very valid. What I do personally is I thaw chicken meat (thighs in my case) partially in the microwave, then I slice it into 1/2" (about 1.3cm) pieces across the grain before cooking in a saute/stir fry of some sort. I like partially rather than fully thawing in the microwave because it gives a better taste/texture than a full thaw in the microwave, and it is very easy to slice when partially frozen.