Airlines may ask for proof of onward travel if you haven’t booked an RT ticket with them. They might waive the requirement if you say you are traveling by bus to e.g., cambodia, but getting a dummy ticket might be good for peace of mind.
She will also likely need to get a CFO certificate from the Commission on Filipinos Overseas, which is a process in and of itself. There are other requirements as well.
I suggest you and your GF join the LINT group and really read up on requirements:-