Your girlfriend should go to the NSO in Manila and ask for a CENOMAR which is a certificate of no marriage. Because the Embassy will require this should you ever apply for a visa/marriage license. if her CENOMAR comes back as "no marriage recorded" then you dont have a problem. If it comes back as married to XXXXXXX then that marriage will have to be annulled before you two can get ever get married, even if her recorded marriage is fake and the husband now has 20 wives! Why is that? because the marriage has been recorded at the NSO and only an annullment will undo that record making your girlfriend able to marry somebody else. The good thing is that if the recorded marriage is fake (as my wifes was with a fake marriage license) then the annullment is straightforward.
Annulment is not cheap (>£2000 three years ago, even for a simple case) in the Philippines and can take up to a year. We used an attorney in Manila called Jeannie Pulido, she was great.