My gf’s (or i’s?) 3DS wireless connection exploded

Hi ! Please if you can help us you would save our christmas, something terrible happened… I have a new 3DS XL (modded) and a few weeks ago, i modded my gf’s childhood 3DS. But it seems that this problem is completely unrelated to the modding. Everything worked perfectly fine, until today. Local wireless connection doesnt work anymore and i cant figure out why, it was still working yesterday. It is ON on both of our consoles, we have the same region, time and date. It seems like the information is sent to my DS, but it doesnt get back to hers. For example, when i create a mario kart party, she can’t see it. But when she creates one, i can see it but when i join it, it says an error occured. Same for Pokémon Soulsilver, and for mario bros 2. We played these same games together just yesterday and it worked, nothing special happened today so i really dont get it… Thanks for reading me i really wish there’s a solution to this