Are you sure you or she haven't missunderstood something?
IF she realy BOUGHT it, then she is owner,
although there can be
/depts the old owner had, but of a type which follow property (as e g property tax, electricity.)
BUT such are paid to BIR, DENR, electric company, the barangay and such. As far as I know there are no such to NHA.
The only I can think of POSSIBLE to NHA is IF they handle some building inspection.
Or has the Property been FORECLOSED and your girlfriend's family was owner BEFORE the Foreclosure?
There is some public office involved DECIDING the cost, when it's "buy back" situations, but I don't remember if it's NHA and I don't know if the involved public office just decide the cost or if the pay go through them too to the old lender.
BUT it's ODD this question wasn't BEFORE she renovated...
Have you supported her much to the renovation?
If so I start being suspicious she try to scam you at more money...
To judge what can be such amount:
How much was the buy price of the property?
Is it titled?