The toy is probably fine to leave in the tank for short periods of time while your animal interacts with it. Some soft plastics and rubbers have compounds in them that are similar to animal protein and fat molecules so your octo may try to eat the rubber toy (this has happened to me with rubber fishing lures that look like fake crabs that I was using for a hunting behavior study) so I would keep a close eye while your octopus is interacting with the toy.
I personally don't believe that toys are strictly necessary for octopus enrichment so while I don't think your animal needs the toy to have a good life, if you are really set on letting her interact with it then it is probably fine for 20-30 mins every couple days.
Again, its your decision to give her the toy, I don't really think it'll cause problems but keep in mind that anything in your tank environment that is not from the ocean can cause a risk to your animal.