One of the challenges you might face when caring for a senior is their own resistance.
First thing on the way to deal with it is understanding the reasons they do not want to be helped. They might feel weak and frightened adjusting to the new way of things or it hurts their pride to understand they can’t do it alone anymore. They can simply not understand why they need any care in the first place.

Sit down with them, when you both feel calm and are in a good mood. Discuss the reasons you think it would be better if they let you help them. Make them feel as though you need this as well in order to know they will be fine.
The most important thing is not to give up. No matter how stubborn they are – they need your help.