Yevamos 109b - Kiddushin as a Ketana Turns into D'oraysa

The gemara has a tzad to explain r' gamliel, that the original kiddushin as a ketana develops somehow into a kiddushin d'oraysa. Rashi seems to indicate that when she turns into a gedola and does not do mi'un we retroactively turn the kiddushin as a ketana into being kiddushin d'oraysa (similar to a ger kattan who is not mocheh as a gadol, so that retroactively we consider it to be a zechus and was therefore a geirus d'oraysa). However, Tosafos seems to indicate that the the kiddushin accepted as a ketana is not going to be retroactive, rather will be automatic, without a new act of kiddushin being required as a gedola.

Rashi's approach explains better the reason why it will uproot the zikah, since the kiddushin was retroactively chal before the zika. But, it is very difficult to understand how the kiddushin could possibly work retroactively since at the time she received it she did not have a yad to receive the kiddushin, nor was she a bas da'as to consent to it.

Tosafsos approach explains better how the kiddushin could work, as tosafos ha'rosh explains that if the kiddushin is not going to be chal, the money she received should have to be returned, therefore, that money that she received and is not returning turns into kiddushin d'oraysa as soon as she is a gedola. However, it is difficult to understand how it can uproot the zikah since the zika will still be chal before the chalos of the kiddushin.