Can a person wilfully hide a will fr siblings

If your mother has passed away, then no, your sister does not have any right to hold the Will. If she won't offer it for probate (which will require her to provide you and your other siblings with copies), then you will need to get a good probate attorney who works with estate and trust litigation (I don't do litigation, by the way) and file a petition with the probate court asking them to compel your sister to produce the Will. Best wishes to you.