You can have fundamental discussions on meta-levels, no question, but unfortunately that does not help Kati's real situation at all. She recently found out that the new construction is unexpectedly more expensive, even though she had already anticipated price increases. The (at least) same effect applies to the value of her current property. Why buy new expensively and sell cheaply? Then she loses twice.
However, you cannot consider the individual separately from the whole. Individually, I fully agree with you – sell expensively, build new as cheaply as possible. Logically, everyone wants that. But that requires double the luck. Because there is no automatic mechanism. It could very well be that this endeavor will end up costing a lot of extra money and be financially unprofitable.
You can recognize this by the fact that free rental housing construction is currently almost dead, and also with the construction of condominiums, due to the desired returns for all parties involved, things look pretty bleak. Prices are rising, yes – but the volume is not.
Regarding the approach here – why should she start immediately with a bidding procedure? These are just preliminary considerations; one can certainly test the market locally and launch a sales intention. Bids will come in without immediately having to rely heavily on portals.