Maybe make sure she gets a small physical item that will remind her of the trip. Something she can see now so that she will be able to recall what it looks like when she loses her vision. Maybe something like a pin that’s pretty tactile and has a distinct shape to it or something. It probably doesn’t have to be big either. Otherwise, more in line with your question, I agree that a video recording will probably be fine and describing the visuals through text may not be necessary but it couldn’t hurt.

Just record a normal video with your phone. You can also write down and describe the encounter and visit so she can read it later. It's hard, even for a sighted person to remember details of events. A written memory plus the video would be great.

I am totally blind and do a lot of audio blogging/sound scaping one or the other two different things so audio may work. The idea of a physical item is also a good idea. I like tactile things from gift shops.