I'm nearly 65, your mum is 66, not 106.
I'm currently receiving immunotherapy treatment for skin cancer and can't go out at all, except for essential runs to hospital for treatment and blood tests.
I haven't seen my 7 year old grandson for a month, except through a closed car window on my way back from treatment 2 weeks ago. We What'sApp video each other every night though which is great.
You mustn't give into emotional blackmail. My mum was a wonderful woman, but prone to that herself - 'Look what I've done for you' etc. etc. Your mum sounds depressed - laying on the sofa all day isn't normal behaviour. If she won't seek help herself, there's very little you can do as her GP would probably say they couldn't talk you you without her permission as that would be breaking patient confidentiality.
If you feel you have to see her in person, go to her house and stand at the end of her path with your toddler in the buggy and have a chat, or she could go to yours, but I agree with other posters - don't let that extend into either of you going further up the path and ending in a visit inside the house. Don't go for a walk together either as you can't be sure she would keep to the social distancing guidelines.
You would never forgive yourself if you, your little one or your mum caught the virus, so stick to videos until things improve.
Good luck.