You can help make things easier by having the temperature, sg, pH, etc. as close as possible.
The idea of setting up the same aquascape in the new tank is a good one - of course, the tank is bigger so you'll have more, but maybe a corner could be the same.
We've had a number of people move their octos to new tanks, so it can be done.
If you use a cup or container, make sure you've rinsed it well in distilled water or salt water so there's no soap or detergent residue.
You may have to remove some of the water to be able to catch your little octo - is her den in a rock so it could be picked up with her in it?