Question one should ask is how much is she paying for her next HDB? The paper is being irresponsible by giving the impression that the owner now has $420K to spend as she wishes, buying her next home at the same price as the current. Anyone with basic intelligence will tell you sell high, buy high, sell low, buy low. For all you know, her next home cost more than her current and she is incurring more debt.
This kind of article is very misleading. In every HDB flat transaction, there cannot be just one owner. Either husband and wife buy together or some other family members buy together. Therefore, when you sell the flat, you have to split it up between the registered owners. SO, in this example, if 2 people bought together, then each make only $210K. If they added a parent to the initial purchase to qualify, then it has to be spread threeways, and so forth. The only exception to this is if he/she ended being the sole owner due to the death of the other registered owner. This is one of the few real advantages to the HDB flat scheme, i.e. the right of succession transfer with no penalties.
In actual fact, after the owner adds up all the interest he had to pay out and any mandatory upgrades, and property taxes, resale levy, initial reno costs, etc. I can assure you he is well short of the $420K mentioned. If he can net out $300K, and split half, he will only have $150K in his pocket/CPF account.