@jcsc not meaning to pile on but you need to get a clear picture of who this person your daughter is actually in a relationship with.
Is the GF known to any of her real life friends in real life or to they just know her from online/social media?
Have they ever face timed? It’s very easy to set up fake social media using someone else’s photos.
What dad would think it would be appropriate to message a 14year old he’s never met and say his family loves her? He’s either got no boundaries or isn’t real and is just another account created by the ‘GF’.
Catfishing is very real and very easily done. Those who are very invested go as far as creating other personas to help make their main character feel more real by having ‘legitimate’ seeming connections to invented friends and family.
It is extremely unwise to allow children to have access to social media you don’t understand or have oversight of, they are just too vulnerable to make decisions that potentially could have significant impact on their lives.
If the GF is who she says she is you need to cut your daughter off and get her offline for a time, instead focusing on real friends and potentially getting her actual friends on side.
in the longer term I would be restricting the social media she is allowed to use or learning how but all works. She is so vulnerable to emotional manipulation and being pressured into sending explicit photos. If she has fine this and there is evidence you can report the GF to the police for having indecent images of a child.
I would be looking for resources to teach your daughter about coercive control and abusuve relationships, she’s young but she’s entered a world she’s not mentally or emotionally ready for and needs help, whether she wants to accept that or not