Ip connects for me but not for my friend

We set up the server on vanilla and it worked fine for both of us. We switched to craftbukkit since we wanted to install plugins. Now the ip works fine for me(no matter if I use localhost or the ip she's supposed to use) but she can't join (getsockopt message). The ip checking websites also give me mixed results somehow. Pokapoka.pl (website advised on the forum for my specific router under a question about a mc port) says the port is properly set up but canyouseeme.org can't connect. According to every port tutorial I found it should be working (tcp/udp 25565 port) the tutorial for my router also advised adding a stative ip address (that one also doesn't work for her). I'm playing on 1.21.10 version