Noemi's Malou 4/18 Type III disc -BichonFries mix- Germany

Welcome Noemi! First thing to know is that your young pretty girl, Malou, can live many happy years ahead! 

Give her the chance and time to heal her nerves to the extent possible. Malou, like all dogs, focus on the right now not the past nor future. If she is out of pain, getting yummy food and love from the both of you, and a warm place to sleep, she is happy.  

In time, if she would need a wheel chair, she'll focus on enjoying having the wind blow her ears as she runs in a wheelchair.  But I get a head of my self here.  Let's deal more with her current situation to make sure we fully understand before giving your comments for the right now.

Can you verify for us about the Type III disc and what your neuro said:
--- Did the CT and MRT both demonstrate there were NO COMPRESSIVE LESIONS on the spinal cord?   If no significant compressive lesions, then physical therapy could start right away. Meaning the compressive lesions would not give any risk to causing further harm to the spinal cord.

--- Did the CT and MRT showed a compression lesion on Malou's spinal cord?  Starting physical therapy with a compressive lesion present means Malou may get worse and never have the opportunity to self heal the back legs and bladder functions. 

EXPRESSING THE BLADDER
Usually catheters are as a last resort.  Examples would be a heavy dog where it is very hard to feel for the bladder to be able to manually express, or could be the area of the spinal cord that was damaged makes expressing difficult, etc.

What was the reason given for cathing rather than giving you a hands on top of your hands demo type of expressing lesson on Malou?

Malou is on drugs which help with expressing!
    Dibenzyran (Phenoxybenzamine)-  Decreases internal urethral sphincter tone. Makes the neck of the bladder easier to open when the muscle is not so tight.
    Myocholine (Bethanechol) Enhances detrusor muscle contraction. Allows the wall of the bladder to better contract and push urine out.

Most dogs are sent home with an expressing lesson for health reasons to prevent urinary tract infection (UTI). Unless there is a difficulty reason that calls  for the catheter, ask your local vet or the neuro's tech to give you that hands on lesson.
  First review the video and tips so you get more out of the lesson.  dodgerslist.com/2020/05/05/bladder-bowel-care/

Have you tried expressing for poop? Expressing for poop is so that before mother nature would just let it plop out anywhere, you get there first to encourage poop to clear from the digestive tube to plop out where you desire. Most of us express on the toilet: upon awaking in the morning, maybe at 1-2 pm during the day and again before bedtime. First you should make a chart of eating, poop plopping times and try to figure out when you should be expressing. You really do not need anyone to demonstrate how to express for poop. This video shows how easy it is:
Helpful tips: dodgerslist.com/2020/05/05/bladder-bowel-care/#poop