In what way doesn’t he treat her that good? It sounds like your desire to be with her is clouding your judgement of him, in which case you should not home-wreck, but if he legitimately isn’t treating her well, even if there was no possibility of her being with you, then yeah, as a good friend, you should tell her that she deserves better than the shitty treatment from her boyfriend (not necessarily you though).
Honestly ion know if it’s worth it man I mean first if she doesn’t realize how bad he treats her she obviously likes him a lot plus since he’s long distance what’s stopping her from still being emotionally Available for him I mean if u want her to see u gotta start with the little things till she realizes but don’t be weird abt it u got to be just be normal if she notices she does if not she doesn’t 🤷