Japanese speakers, I need your help?

[bcnu]

How would she possibly know about your "photo of a souvenir" if you have not posted (distributed) the photo or its translation anywhere?

The best, polite response would be a short apology, denial of intent to cause harm, and promise not to do it again. Arguing about having some "rights" to it could simply enrage them.

First, using the excuse that you have seen others "tweeted and posted online for years" has ABSOLUTELY NOTHING to do with whether you are about to be sued for copyright infringement.

Second, "giving credit" is not a license to use any of the exclusive rights of the copyright owners, including distributing photos of it or making any translation of it, both of which are "derivative works".