LN explains better but he forgot to mention that not only does a person feel heavier as time passes but towards the end of the third day start turning to stone. Person can fully recover if removed from dungeon before turned completely at end of third day although will need a few days to convalescence. Also, those light stones they're using aren't goods from a supply shop but from those two caves where got the level reset and stat boost modifiers. Don't remember if new ones eventually grow back or if once gone are gone for good since nobody knows how to make them, but as long as only take a couple there'll be enough for the rare few lucky enough to find those places as need to use one for the benefits. In any case, wonder if MC knows girl and if she explains how got there next chapter? Her gear looks to be of good quality but expensive due to combining practicality with being a good looking matched set so likely well off. Although unless a complete noob who has no idea how to use equipment or plan things she should've had sense to be in a well balanced party so unless they're in the web pouches that got crushed where are they?
Agree with monkey123, MC is wishing for a healer type with good personality for party and happen to find this girl all alone in dungeon. Could be wrong but clothing seems to be me something a dual class type would wear like a swordswoman and either a holy job or light magic user. Would really be insane if they happen to know each other from five to ten years ago when he was adventuring with his old party. Like his party and her party were rivals for a previous egg, both failed, but maybe due to an intense monster battle or some members having similar interests got along and parted amicably. In any case we'll find out once she wakes up unless she has amnesia.