I couldn't even find it much earlier until now. This is the answer to your problem, Fukuchi, using two different sources, one from U.S. embassies.org, and another upon searching Indonesia marriage permit age.
The Marriage Law 1974 permits women and men to marry at 21 but allows girls to marry at 16 and boys to marry at 19 with parental permission. Parents can also ask religious courts or local officials to authorise marriages of girls even earlier, with no minimum age in such cases.
Marriage in Indonesia requires a religious ceremony. Indonesian law requires that both parties must be of the same religion and the marriage must conform to the laws of the countries of the parties involved. ... The KUA will issue a Marriage Book (Buku Nikah), which is evidence of a legally valid marriage with a Muslim.
Considering that she's aged enough (17 or 18), and you're probably in the 20's and still living in country at the time of this post, ensure that both your family's and that of her family's parents are consentable first to do this and then arrange a formal ceremony, but given the parents' power to waive an earlier marriage limit, this might be fitting for your case, maybe. Such a marriage like that in highly religious countries is lifelong and permanent.
Hope this understands it clearly now.