My grandmother has Alzheimer's, and l recently saw a Dua for memory. But we don't speak Arabic and she wouldn't know how to recite it. Is it okay if I recite it for her and blow over her? Is that bidah?

I highly recommend that you do not make up practices for which you have no evidence in the Quran or the Sunnah. If you want to perform ruqya upon it, just do the legislative ruqya rather than looking at certain du'as and using them as ruqya when we have no evidence for them.