Welcome to HCM
Your mother is diabetic with CRF with Hypertension
, hope her BP is also controlled ,she appears to have some kind of obstruction to out flow as residual urine is 300ml .
It is advisable to visit a Urosurgeon and get a Cystoscopy
to know the cause of obstruction and then a CMG study to find out function of bladder muscle may be required and once cause is known she can be treated accordingly with medicines or any required surgical procedure.
Good luck to her.