i have a friend and her flight is 8:05 in the morning at the HKIA if she take the first train can she catch

I think she can catch the first train to HKIA.
The first train from HK Station is at around 05:50 and it reaches airport in around 24 minutes later.

If she want to check-in advance, it is possible. She needs to go to the HK or Kowloon Station to ask whether the airline company can provide the advance check-in.