Hi Phil. in this case, if she's using a Philippines number in China, you'd need a calling plan for the Philippines. She'll receive the call wherever she is, and she's responsible for any roaming charges she may incur.
The great news is, there's a very inexpensive way to call her. I've documented this in other threads, but I'll summarize it quickly here:
Do a websearch on "free UK numbers"
Create an account on a website, grab a UK number. Set it up to forward to your girlfriend's number from the Philippines. If she has a number from China, works just as well.
Save the new UK number in your contacts under your girlfriend
Add UK 1,000 minutes for $20 per month to your Koodo line.