Some years ago the ladies in my neighborhood hovered around a man who was recovering from a
stroke and asked me to help him. I talked to him and his only request was that I go buy him some whisky to help him cope and deal with his pain. so I went to the liquor store and bought him two
bottles every week. We all do what we can...

walking with her - however well or poorly she manages- is the very best thing you are providing. Strokes are a strange thing...she may be using all her strength and attention to manage the walking she already does with you. An attempt to increase her stamina thru a step up motion or similar might be more detrimental then helpful, just balance wise. You said she has no use of her left arm and limited left leg ability, but she is probably using all her strength to use her left arm to just steady her gait on the walker, for each step.

If she is right handed, or even left handed she might have had a lifetime of leading her stride with the left foot. To use her "stronger" right leg might seem like learning to walk all over again.

I would strongly suggest sticking with whatever the physical therapist says, not try to push something on your own.

Again, I applaud your willingness to want to help, but maybe just the willingness to walk with her is the very best thing you are doing.

(I have no expertise to arrive at that advice, but my son is a physical therapist, and I've spent a lifetime around people with disabilities, for whatever that's worth.)