Create an email address for your niece, Put the digital data into an archive format, then email the data from your niece's email account to your niece's email account. I used to do it at college to backup my work when i forgot my usb stick. 2 years on the data is still there.
There's a simple solution to this problem which no one has apparently figured out yet.
Give her a mop and a bucket and stick her in the kitchen then go for a drink, if its spotless by the time you've come back then you can be damn sure that he/she is female.