Mother daughter dance

The problem is that there's no way to know if it would hurt her to dance to "their" song with you at your wedding. I would ask her if she wants to dance with you and if she says yes, then ask about the song.

We lost my dad six years before I got married and I danced with my brother to the song from which my dad got his nickname for me - and my mom *sobbed* the whole time

The idea is fine, but not as a surprise. There is too much risk of your mom being more sad than happy at being blindsided by a special song AND a spotlight dance at your wedding.

I’m doing a “surprise wedding dance” you could say with my mama as well. She knows about it, but it’s a surprise in the sense that she doesn’t know when it’s going to happen (only my DJ, photographer and I know that) but I recommend you choose a song closer to the two of you and your relationship with her. You can honor your late step father in many other ways such a memorial table with a photo of him on it. You could also get a charm to put on your bouquet with his photo in it as well. But, in the case that it would sadden her more than it would make her happy I would choose a different route

I choose momma song by Carrie Underwood, it’s a beautiful song