A person is arrested and detained and then must go before a judge within 48 hours to have a bond hearing. usually, that occurs within 24 hours when the probable cause hearing is held. So, your mother has had a bond amount set in her case and could get out of jail if she posts bond. No bond, no freedom.
The limits to her being held without a sentence are based on her speedy trial rights. For misdemeanor charges she must be brought to trial within 90 days, and for it is 175 days for a felony. Speedy trial dates exist just so authorities do not hold someone in jail for "excessive" periods of time without litigating the case in some form or fashion.
So, to answer your question, which does not contain many facts, they can hold your mother in the jail until she either makes bond, takes an offer and completes her sentence, or goes to trial and either wins or loses and completes her sentence. Try to contact her lawyer for more specific answers. If a public defender, try making an appointment to go see him or her in person. Good luck.
If your mother continued her case then that should also mean that she waived her right to a speedy trial. Therefore she will be held until either she posts bond or completes her sentence. Technically with a wavier of her right to a speedy trial, her case can be continued indefinitely.