I'm sorry to hear about your situation. Yes, you do have some rights. That is, it's your decision unless your ex can prove that there's a significant likelihood of harm (to overrule your decision). Now if an evacuation is ordered, then it would be reasonable for her to assume that there's a threat of harm. But if no evacuation has been ordered, and based upon the actual situation of your house (brick vs siding, high vs low, etc...) then that would most likely be up to you and she couldn't override that.
Now as a practical matter, if she were to hold your daughter back for the duration of the storm, it would be up to a judge to determine what, if anything, would be the penalty. It might be that the judge finds that there was no good cause to withhold the child, BUT in light of the circumstances that it would still be forgiven. That's an entirely plausible outcome for a contempt action arising from this. Or the judge can really throw the book at your ex, if it's objectively unreasonable to withhold your parenting time. But the more likely scenario is that the judge would say that it was reasonable under the circumstances, and impose little, if any, penalties on your ex.
Now you can still threaten your ex if she does this, but such a threat would be (as is explained above) mostly a bluff. The time and resources to file a contempt action would take months and money, and unless it can be objectively proven that she was acting so unreasonably as to punish her, the judge wouldn't do so.
I know this is probably not what you wanted to hear, but it is the law. I hope that clears things up anyway. If you have any other questions, please let me know. If not, and you have not yet, please rate my answer AND press the "submit" button, if applicable.
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Thank you, ***** ***** luck to you!