Driving without a valid license (because you never had one, it was expired, etc.) is a misdemeanor [or it can be an infraction]. A misdemeanor carries potential jail time and fines. Driving without your license in possession is an infraction. It matters what she's being charged with.
It she was cited, she should have signed the citation and a written promise to appear on a certain date. If there really is no date on the citation, I'd suggest contacting the court ASAP (they're closed Monday for the holiday) to see if the citation is filed with the court and what the appearance date is. If she misses the court date, a warrant for her arrest can be issued, the fines can go up... it just gets worse.
If she lives out of state, an attorney can appear for her and handle this situation.
From there, it really depends on what she's being charged with. If it's a misdemeanor, she'll need an attorney - either one she hires or a public defender appointed by the court. If she needs a public defender, she'll have to appear in court to request one - all the more reason to find out what her court date is. Double check the citation to see if you can sort out what she's charged with and her court date.
Or you could contact a local criminal defense attorney to let them get this handled.
The best thing your sister can do is contact the clerk of the court and see if the matter has even been filed. It takes time for a traffic citation to make it into the system. She needs to appear in court on, or before, the date on the bottom of the citation where she promised to appear apparently there was not one). If she fails to to appear a Failure to Appear will be added to her problems. With an fta she will have problems with renewing her own licnse in her state. Hiring a traffic ticket attorney might be the best option. The attorney can appear and deal with the "no license " issue without the need for her to be present.