13 year old niece acting strange while over to visit this weekend? How do you talk to a teenager?

Occasionally family comes down to visit and normal outdoor bbq activities go on.. Well this time while i was doing some wood working and in my care was my 13 year old niece because she did not want to go to park with the rest of family so she stood behind.. I noticed she untied our german shepard with the leash so i thought she was taking him for a walk and payed no attention.. But then about 20 minutes later seen her squeezing out of the garage with the dog still on its leash.. I asked her is she had taken him for a walk and she nervously replied " he ran in here and I could not get him out". So I asked her if she wanted help chaining him back up and she said "no I got him". So she chained him up then went straight for the shower... Not sure if I should look into this further or if this is something that I should be concerned about or if this is none of my business? How do you talk to a 13 year old teenager? I just want to make sure I am not allowing her to do anything wrong? I realize this may be around the age puberty takes place.. Any info or advice is appreciated.. :)