I know you are asking for technological tool for this, but looks like the problem you are trying to solve is created by technology , so maybe the solution is non tech and getting away from the technology.
Creating safe situations where she was forced to speak is the #1 technique to treat that condition. The speech therapists used situations like going out to buy ice cream to get her to speak.
So, yea, think of situations that are comfortable but will force you to speak. It's a very effective technique.
Volunteer to host/speak at a meetup?
This could be nerve wreaking for someone who is just getting started. Improv maybe? I dunno.
The meetup crowd, usually, is really cool and understanding.
I was actually thinking of other volunteering events. Soup kitchens, building houses with habitat for humanity, anything really that's a group activity.
Team sports as well.
Could you talk more about this? I have little to no anxiety about public speaking, but hosting a meetup sounds like a lot of work and stress to me. Are you talking about putting a new meetup group together from scratch, or asking a preexisting meetup group if you can MC for them one night, or some third thing?
Hosting a meetup is indeed a bit of extra work (I have just read the coordination notes our HR sent out, and oh boy...).
Offering to do a talk at an established, not too large meetup should be easy. Only the biggest and best known ones can pick and choose their speakers. Everybody else has to hunt, sometimes even beg for talks. As a result, these "lesser" meetups tend to be more casual. Nobody expects a professional, conference scene level of presentation.
So as long as you find a meetup that suits your taste, offering to do a talk every now and then should be more than welcome.
I was reading a piece on psychological mutism and the writer stated that the worst possible thing to do was attempt to force the child in to situations where they had to speak. There reasoning was that this lead to stress which increased the chances they wouldn't speak.
Sorry I can't cite the piece as I've lost the reference.
You're perhaps leaning that way? It hinges around what you mean by "force".