I think I’d ask her if she’d like you to do it. I know she said she didn’t want your help months ago, but that wasn’t in the midst of a storm, was it? By asking, she has a chance to say no if she’s still adamant (in which case you just say a cheery “ok” and go back to whatever you were doing) or she’ll say yes and you’ll have a chance to remind her how thoughtful you can be.
I wouldn’t do it without asking though. She might interpret that as you not taking her seriously.
