I think you can put a positive spin on. Emphasise that it will be fun and that it's going to help her to make the words she want to. You can tell her that you want her to be happy and you've noticed that not being able to talk as well as she likes makes her feel unhappy sometimes so you've found a nice person to help her.
As far as I know a lot of it is teaching parents and children excercises that you can do at home so it's for you as well as her. They try to make it fun so after the first session she'll probably look forward to the next one.