i praise her and say "YES" "GOOD GIRL"! EVERYSINGLE TIME!!
I think you need a bigger party when she goes outside. Bring treats and make a huge deal of it. Lots of praise lots of treats immediately after she goes. Also, don't let her out of your sight, each time she goes inside reinforces the behavior. Recognize her body language when she's about to go and get her right out.
ADCH Mikko (USDAA) SCH-B; (NADAC) EAC, EJC, TN-E, TG-E, VerO; (AKC) NAJ, CGC; (NACSW) NW1 - 9 year old GSD