How should I deal with such matter?

Hmmm correct me if I'm wrong but it seems like your helper is trying to avoid the medical checkup result? Am I reading between the lines properly or looking too much into it? Anyway, if I was in your shoes, I'd be okay with letting her go back but only after all the loose ends are tied up, in this case, the medical, the thumbprint and a replacement. Maybe you should also seek advice from the agency from which you hired her from, see if they can help. To me, if my helper has been with me for years and is trustworthy/loyal, I wouldn't mind letting her go home for a week but if she's new or you don't really have a good feeling about whether or not she's coming back, then maybe it's time to consider other options.