Those not born in the US may speak differently, and that's ok. They may have to adapt a bit so as not to alienate people.
The first rule in etiquette is not to offend. We need to be mindful that every situation is unique. Rarely do broad brushes cover every circumstance. However, we can generalize that telling someone their communication style is a turnoff, could offend them in several ways.
If you point out to someone how they communicate — too strong, too loud, too weak, or too quiet — and then speculate that it's because they are foreign, it could send a negative message. That they are also different, don't fit in, maybe even that they are not welcome because they're "other." So, decide if you want to talk to your colleague about this.
Is your colleague's communication style so off-putting that she is alienating others and holding her back from promotions? If yes, and you have a good relationship with her, you could consider mentioning that the current corporate climate expects a more subtle communication style than she uses.
For example, you could preface any conversation by telling your colleague that you have great respect for her and her work, and you would like to see her have the same opportunities to advance as everyone else in the firm. You can delicately add that her very direct, "in your face" style of communication can seem too aggressive for some in the firm.
Your colleague's style, like yours, is an accumulation of instincts, character, background, and culture. Telling another person that they need to change "who they are" is daunting and insulting. You need to be respectful and empathetic when advising someone to "change their style."
So, consider her feelings, and politely tell her that reasonably adapting her communication style and toning it down could help get her message across more successfully. Make it clear that she should be authentic, just a bit more subdued.
Many people are in a similar situation as your colleague, regardless of their origin. Their styles, for whatever reason, do not match the business climate in which they work. It takes a lot of self-awareness to realize this, and it's always best if you can see this in yourself before someone brings it to your attention. Emotional intelligence plays a big part in this scenario, and you want yours to be high.
But sometimes it's hard to see qualities in yourself; our self-perception can be a bit skewed for myriad reasons. In this case, if a colleague politely points out that your style is not an excellent fit for the company, be grateful. Your coworker thought enough about you to point out something that could stymie your career.
Ultimately, stay authentic but be aware of situations that require you to adapt reasonably to be respectful to your colleagues and to the organization. Knowing when to adapt is a skill that you can learn, and it will help you to advance throughout your career.