Have your RPi text you her IP on startup.

This script belongs in /etc/rc.local, but make sure you're not completely replacing it. rc.local runs after the rest of your stuff has been set up after booting.

If you have other stuff going on in your rc.local, add the following lines before the final line that reads exit 0:

# Print the IP address
_IP=$(hostname -I) || true
if [ "$_IP" ]; then
  printf "My IP address is %s\n" "$_IP"
  IPADDR=$(ifconfig | grep 'inet addr:' | cut -d: -f2 | awk '{ print $1}')
#  replace NUMBER with your cell #
  curl http://textbelt.com/text -d number=NUMBER -d "message= $IPADDR"
fi

Replace "NUMBER" with your phone number in the format 5555555555 (don't include the +1).