She being old ,there are more chances of Presbycusis(hearing loss
in old age).
Or it may be because of some drugs whose side effects are hearing loss.
First of all you must get Ear cheked by ENT specialist
who can see the ear drum in OPD by an Otoscope
and tell whether there is wax or not.
If there is wax you can put ear drops for five days so that the wax gets softened and then can be easily removed in OPD by-probe ,syringing,or suction cleaning under microscope.
then get done a Pure Tone Audiometry
(Hearing test) which can tell the type of hearing loss.
then further management can be decided like-If conductive then she can take some medicines which may help.if Sensorineural then she will need a Hearing aid