Mine gets worse with each pregnancy.
The only time I get concerned is when it interferes with my ability to consume calories or hydration. I say "calories" b/c I decline so quickly that it became an issue of finding what would stay down and then finding things that had some substance to them even if it was crap food. (for a whole week, donuts is what I ate--and it wasn't preferred...it was simply survival! And I still lost weight-- a first for me with any pregnancy!)
From a health standpoint, it isn't a big deal until it gets to the point of hyperemisis. Then it is critical to watch for the proper symptoms that necessitate a visit to the hospital for either quick IV fluids, or even a mutli-day stay to get the mom stabilized.
As with any human--lack of food and water will eventually result in health consequences.
And oddly--for me it doesn't matter if it is a boy or a girl and all mine are singletons. I was stuck in bed for 6 weeks this time and still wake up on some days not wanting to do anything.
However, I have been barf free for over 48 hours and am just trying to navigate nausea at this point. (I'm sorry for TMI--but it is cause to celebrate as I have been sick for almost 2 months now.)
If she is concerned, she should not hesitate to mention it to her doctor. With my first, I felt I was being wimpy--but with experience, excessive vomiting is nothing to play with.
ETA: Morning sickness is typically a sign that the pregnancy is progressing along fine. It doesn't mean that nothing bad will happen, but it is usually reflected upon as a good sign.