Why doesn't she get a second phone/line for business only. If someone abuses that then at least they don't have her personal number and she can deal with the inappropriate use of her business number accordingly.
She could also make it clear on the card that it is a business number.
It doesn't really matter, I've had an ex get asked to dates over email by potential business leads. Especially awkward is the "half and half" situation where they asked you to dinner to discuss business. For her it was especially hard to turn down because it wasn't just a networking client is was often a potential client for her firm.
The point is you take steps to separate your business and personal details so that some percentage of your encounters will get the picture.
For those that don't, you should be able to deal with them quite candidly. If they persist and start harassing you then block their number or report them.
If you can't do this, then maybe the problem lies on your end. Stop putting yourself in the position where you are helplessly being tormented.
How does that make a difference? All numbers are the same to predators haha! I doubt she advertises the number on her business card as a personal one anyway.
She could also make it clear on the card that it is a business number.