Speaking to my French partner this morning, she told me everyone used to track the state of the economy by the price of a baguette (seriously, this is not me making fun). Right before France switched to the euro, apparently the price of a baguette was 1 franc. Then after the switch, it became 1 euro. But the value after the conversion 1 euro was about 15 francs. So a basic foodstuff suddenly cost 15x more than.
So how did European citizens handle the conversion switch and did it cause huge problems for citizens through the value disparity?
You're asking a very broad question on which a single answer can only be given if you narrow it down first; maybe by focusing on a specific population group or nation. Can you help there?
I can go into the bread statement already: Your girlfriend might be misremembering something about the bread prices and a perceived "value disparity". In fact the conversion was very close to a 1:1 value on bread.
Until 1987 the price of bread was government regulated in France. Starting on jan 1 '87 this was deregulated in order to promote fair competition but it gives us a good idea of prices all over the country. At that time the costs of a 250gram baguette (Paris region style) was about 3 franc. If we exchange that to the (at that moment non existing) euro rate that comes to about 2 euro per kilo.
At the time of euro introduction in 2002 the price of one kilo bread was about 2,7 euro (source Insee). In the last French franc month it was about 2,69 euro per kilo, or 17,7 French franc per kilo / 4,4 French franc for a 250gram baguette.
Sources:
Formal fixed exchange rate at the time of the switch (jan 1, 2012) €1 = FRF 6.55957 (French francs)
bread price per kilo on Insee https://www.insee.fr/en/statistiques/serie/000442423