M.R.
K.,
YES! Our daughter did not speak at mothers day out. She was also very shy, but the problem turned out to be anxiety. If this is the case for your daughter, it may turn up in other areas too, and you will need to do something to help her through it. If she talks at home and is developing language, you may have fewer problems, but for us, this lead to some language delays in expression that still linger today (she is 11). Therapy may be in order, check with your pediatrician for a referal to a speech therapist, and be on the look out for other related issues in her development.
M.