How can I prepare my 8-month old for the time change in nov? I'm worried she'll wakeup an hour early

Slow change. Slowly change the time of sleep by 15 minute intervals. You can do that every few days or weekly until the adjustment is made.
Delay sleep. Gradually adjust your baby to the new time over a few days. Keep her up 15-20 minutes later a week prior to the time change and allow her to sleep longer in the morning. A few days later do the same thing again-put to bed 40 minutes later than before and allow to sleep. And repeat a few days later. Over the course of the week she will gradually adjust to the time change.