[CharlesStevenson]

Have you asked her to try pumping the pedal to see if it gets harder, and then when she starts the engine, whether it sinks to the floor?

If she can build up the pressure that then goes, that's perhaps going to suggest a leaky servo.

I've driven a few vehicles that started doing that to me, scary, but at least I could get home before it was u/s.

It still won't be driveable for her, but it might be ok to be moved if you're going to do some work on it yourself.

Just a thought.