13 month old sucking on AA battery

While I was in the kitchen making dinner I had my 1 yr old crawling & when I went to check on her she had a AA battery in her mouth, I feel so horrible knowing she had that in her mouth, now I’m freaking out & wondering if I should take her to the ER or something !! The battery looked completely fine but the more I looked at it I noticed what I’m thinking is her saliva & i started pushing down & saw what I’m guessing is rust ?? I know I’ll get people on here judging me & saying why would I come on this app asking what I should do but she seems fine & like her normal self so idk if I should be super concerned or not