What is the appropriate size of the urinary catheter for females to prevent urine leakage?

Hello doctor,

My grandmother is 88 years old and is currently paralyzed on the entire body for the past six months now. She is fed through Ryle's tube and a catheter is also inserted since the day she was paralyzed which is changed periodically. My question is that currently, the catheter number which I am using for her is 22.

Earlier I used 18 and 20 respectively. But the problem is that the catheter always leaks and half the urine usually does not go into the urine bag. I do all possible things to unblock the catheter mentioned online in case of blockage in the catheter or the tubing of the urine bag. But the problem persists even if the catheter is new even if it is inserted on day one after being replaced.

I have tried two nurses in case the nurse was not able to insert the catheter properly but it is not the case. So please suggest the size or number of the catheter be used for my grandmother so that it does not leak. The earlier mentioned catheter number (18, 20, and 22) were mentioned by a locally practicing doctor. Your answer would be very helpful.

Please help.

Thank you.

Thank you.