Hi,
Based on my personal experience and few members who shared theirs here,I believe IRCC has slowly started increasing the number of applicants in the virtual ceremony but not like 10s or 20s, still in single digit which is manageable.
I had mine yesterday along with another applicant. But in your mother's case I think it might still be one person only as she is elderly.
As and when she gets a virtual oath invitation, please don't worry the IRCC clerk and judge are very friendly and accommodating as they are aware of the challenges of conducting the oath ceremony virtually. Yesterday, in my ceremony too there were few interruptions due to network problem and they were super cool as it was happening not just on the applicant's side but also on their side.
Coming to the language part, I do not speak or understand French but we were given oath in both languages. I just repeated the sound I heard while taking the oath in French and the judge was saying one or two words at a time so that the applicant can repeat them with least issue and waited patiently for us to complete. But I understand the challenges of an elderly person. While you are waiting for the invite you may want to google and download the oath audio for your mother and practice with her so that she will be confident. Again just my opinion but it's up to you how you would want to proceed. In any case, all the best for your mother's oath invitation and the actual ceremony.
Take care.