Why would my grandmother be admitted to a rehabilitation center when she was throwing up?

She could be vomiting blood, or they see her as having "failure to thrive" which means that she isn't keeping her weight. My guess is that they haven't gotten to the bottom of the vomiting and want her monitored. She doesn't need hospitalization, but she needs professional observation. Of course, without full knowledge, I'm just guessing, but that's what it appears to be to me.
Take care,
Carol