REAPPLY SCHENGEN VISA

Hi guys! I have a question. My mom, dad and brother applied for a Schengen visa and all three got approved. They got multiple-entry. However my mom’s visa validity is different from my dad’s and brother’s. Hers is valid from October 30-December 15 while my dad’s is December 15-January 20. 

My mom will be flying to Germany to make use of her visa. Granting she will go back home on November 23, can she immediately apply for a new visa so she could join my dad and brother on their trip to Germany on December 12? 

Thanks in advance!