Thanks for your query.
Its a very common problem in day to day practice.
Two options are available at your hand -
1. excision biopsy
of that lymphnode and histopathological examination and BACTEC culture
2. Repeat aspirate from that lymphnode for BACTEC culture
This culture will conclusively prove whether your mom has TB or not.
Though the culture report will take time to come. Meanwhile after having biopsy and culture your mom may start anti-tubercular therapy under supervision of a chest specialist and modification of treatment may be needed after availability of report.
Again if it is due to TB then again it is necessary to differentiate between M. TB or non-tubercular mycobacteria
because the incidence of later is now on increasing side and treatment is different from conventional TB.
So BACTEC culture is of utmost important here.