If you test the doll and she fails, the damage may have been done.

Here’s a thought: Can a battery that’s just starting to leak still function enough to appear okay? Then a month you check her again and she fails but it’s too late, the contacts are already corroded. You can do the safe thing and remove the batteries now, or keep her new in box a bit longer at the risk of damage which you can’t fix.

My recommendation: open the box gently, remove the batteries, check to ensure there is no corrosion and then place her back in the box. Your call.