That's especially if changes or suggestions come up without warning. If we have our minds set to some task, we may find it annoying to have them interrupted. We don't take interruptions to our routine our thoughts well. Changes in other ways can be tough or even traumatic too. On one such change a reader asked me about preparing her child for a school change.
Change is a part of life and some changes are set in stone. It's best we know they are coming far far ahead of time. In this case the change can be addressed like a graduation. It should be celebrated and congratulated. If she misses the teacher, you might explain that lots of other kids need her and it's going to be their turn next year. Reinforce that it will be fun to see a new classroom and may even see some familiar faces there.
One thing is for sure. Change should be taught for what it is, a fact of life. It needs to be taught more directly with our spectrum kids than a typical child. Changing grades in school, for example, will mean changing classrooms every year. I have found that it can be shown and taught as a long term routine and thus accepted. Yes, there will be some balking at first, but it will pass.
You can soften the effect of "sudden" changes with timely warnings that they are coming. I do this with time to leave for school in the morning. If I don't, it may take me an extra fifteen minutes to get out the door because he didn't feel prepared for the transition from what ever he was doing.
One might suggest acting excited for good changes, but we on the spectrum don't always recognize your emotions so well. So use direct facts. Is it a good change? Tell us why and how. Tell us that you went through it yourself. Take time to show your child the meaning of change in lifes everyday circumstances. Make it a part of their vocabulary. The earlier that they learn about how things don't always go as planned, the better toward adult life.