All good suggestions above so far. A shower chair is best angled to face the water for obvious reasons, but from your picture, the challenge I see is that she will have to either step in around the shower chair, or face backwards. How much room is between the toilet and tub? Is it possible that she could access the shower from that end? A good exercise for you is: pretend you have a broken leg. How are you going to get in and out of the tub?
We use the following:
-toilet extension to raise the height of the toilet (we have a grab bar in reach of the toilet, but since that is not an option from your picture, I would definitely go with a frame with armrests. Otherwise she will probably utilize the TP holder, which is not safe.
-grab bars in the shower (one on the left where the towel rack is and long angled one in the shower along the wall)
-shower chair with back (ours is free standing)
-rubber grips on the tub floor to prevent slippage
-no bath mats (even the rubber ones can be a trip hazard if you catch your foot on them)
-detachable shower head (with a little hook that allows you to keep it permanently affixed to a lower location, rather than just hanging down in the tub)
-A curved shower curtain rod to allow a bit more space for washing in the seated position
We got the shower chair on craigslist, the grab bars at Home Depot, and my husband installed everything himself, so it really didn't cost too much.