Is it alright for a 13 year old to go by herself for the concert?

No . Absolutely not. Accompanied by a parent of group with adults.

👍🏼

No

I would say no

I dont know if there is any legal restriccions regarding to the age and if they ought to be woth an adult, but if you check this, the environment is very friendly and if you are allowed to go by yourself with 13 years, then there is no problem cause the Mets fans are very kind