The wife should still be able to register a new flat with the
new hubby.
The mother should be old enough to be able to hold her flat by
herself.
The only problem is money.
Chances are, the daughter and mother has a running loan from HDB
and still paying off the flat.
If there is a possibility that the mother can service the loan
herself as well as taking ownership for the flat.
There shouldnt be any problem with releasing the daughter for
getting a hdb home with her husband.