My friend is Filipina and will be in belgium with shengen visa.

Yes, she can. As I know, shengen visa holders can apply Chinese visa in Belguim. Bringing with her shengen visa and other required documents, she can apply at the Chinese Visa Application Service Center. She can pick up the visa on the fourth working day. Express service(Third working-day collection) and urgent service(Second working-day collection) are avaliable there.

There would not be big problems for her to get a China visa in Belguim in three weeks.