honestly just let it happen. i was that friend at one point and it was because i thought that i had to give all my time to my boyfriend because it felt like the norm. i did end up losing all of my friends but when we broke up i came to my senses and realized all i had lost. there’s not really much you can do. but if you actually are set on bringing it to her attention, i would say something like “hey, i really miss hanging out/anything. would you like to spend some time tg?”
You message her and tell her that you love her and loved the friendship and that you are here for her whenever she needs it and you just that her for a while. The reality is women get swept up in finding validation through a man (often emotionally abusive) and all you can do is let her know there someone aka you out there holding the life jacket when she’s ready to jump