There is actually two parts to your question, ie "open email on voice command, or write from a verbal instruction", which need to be addressed seperately.
Voice command software is actually pretty easy, Ultra Hal can easily fufill that need in the "paid version", with appropriate scripts and things to run other programs. However, it cannot control those other programs, which is a big limitation, nor can you dictate (write) into other programs.
The second part, voice dictation, is a bit more complicated, and requires a dedicated software package for resonable accuracy, something like Dragon Naturally Speaking 8. Having actually used the software, I can say that with training, it can indeed get to a very high level of accuracy. It also incudes a text to speech engine to read stuff out. For your daughter, I would recommend a package like that. Ultra Hal, good as it as, is an assistant, not a PC control system, at least, not yet.