Would I be the ah for telling my friend to treat her GF better

My friend has wanted to get with this girl for ages, ill call my friend X and the girl T. X and her best friend go everywhere together. That's fine right? Untill X keeps canceling plans with T to hang out with her friend instead. T lost all her friends becuase they do not like X but X does not invite her to any group hangouts despite the fact we all like T as she's really nice but she is meek. X has started copying everything her friend does in the last few months and dresses and only goes places when her friend does and she seemling values her friend over T in ALL scenarios.

I would be devastated and humiliated if my partner acted like this, particularly not ever hinding neglecting the relationship after being the one who wanted to get with me and if I sacrificed my social circle.

So I want to speak to X and tell her I'm concerned how she's lost all her own personality and adopted her friends one and that she WILL lose the relationship she was obsessing over for months if she keeps on this behaviour towards an objectively nice girl, and that in general she's being a shitty girlfriend prioritising her friend over her studies her relationship and herself, and it honestly seems like an emotional affair to people on the outside.

Ultimately I want to tell her for her own good but I'm not sure if it's the right thing to do.