You could always ask them for an address, and send them a letter. That
requires no proprietary software, assuming you write the letter with free
software / by hand. Then you can include an envelope for the response. Easy.
The only issue is that the stamp may have been designed with non-free
software, and the postal service may use non-free sorting systems. Hopefully,
they don't have any system to read the letter.
This system is particuly good, because even if PRISM crack your system and
read every data packet that goes in/out, they cannot read your letter without
finding it, and opening it. If the letter arrives open, she will notice.
