What's a word for someone who switches off when things don't go their way? [closed]

I have a colleague who has very strong opinions on how something should be done. When it's decided by the group to do it another way, the colleague 'switches off' from the meeting and broods on the fact that we're not doing it 'the right way' (their way) and will often refer back to that fact whenever it's brought up in later meetings.

What's a single word to describe this that will inform them without being too negative?

A neutral way of describing that behavior in the workplace is to say that the person has become disengaged, i.e. not feeling interested or involved in something.

After weeks of Sheila's new manager rejecting every idea she had for improving morale without explanation, she became disengaged and lost her enthusiasm for the project.