This Mew seems completely legit, it's OT is possible, as you can get a Mew with your own OT. (But the event has been over for a long time.) However, if the Mew wasn't obtained in 2005, there is a high chance that it is hacked, because the Mew's OT is "Hailey" which is an OT that isn't possible to get unless it was from the Old Sea Map event. However, you can get Mews with the OT of "Hayley" through My Pokemon Ranch.
Your Mew is probably hacked, unless it was obtained in 2005
Hope I helped!