Help pls my sister is hyperventilating!

Hi. Looking for advice on how to support my sister through her latest break up.

Her reaction seems irrational and unhealthy, but I didn’t date much before my husband so struggling to know what to say or how to help. She lives in the US and I’m in the UK so tough to “be there” for her.

She was married for 16 years before meeting this dude on the second date she went on after her divorce. She’s hyperventilating and hysterically crying off and on (more on) for 4 weeks now. Stalking his Facebook. Puking in the shower...can’t get out of bed.

She refuses to accept that it’s over despite his repeated affirmations. Keeps saying he’s her person. It’s just ludicrous bc while they dated for 16 months, she complained to me a lot about his kids / her concerns with how he’s raising them / how it’s impacting her kids. She kept texting me saying she wants to end it for several months before it actually ended it.