A sympathy card would do. You can sign it just yourself or if it’s the type of office community you could pass it around for others to sign. Other than that, just leave it be. Just l a card or a few words of “I’m sorry for your loss” are enough to show that your heart goes out to her and her family.
I think it’s the fact that it is a change and change brings uncertainty. If you stay where you are, you at least know what to expect even if it’s crap. Changing… You don’t know what to expect.
It’ll be okay. Tell yourself if will be okay. It’s time to step out of your comfort zone and embrace the change. It could be worse, but more likely it’ll be better. You’re doing the right thing.