well i think she wanna use her voice to improve as pratice with u by using voice and sign same time cuz i did that with my boyfriend which he is hearing i do that all the time with him i use my voice and sign and he understood me very well i raise in hearing family maybe she raise in hearing family and have a habit to use voice and sign and maybe she trust u and feel comfort with u that she decide to use voice and sign since u dont make fun of her voice when she dont speak or sound clearly?