If I was alone with her, I'd feel at a loss for words.
Usage notes: usually this happens because you are surprised
at a loss for words
Unable to speak or articulate a coherent thought. I'm so disappointed that I'm actually at a loss for words.
at a ˌloss for ˈwords
unable to say anything: He’s never at a loss for words, in fact it’s difficult sometimes to stop him talking.I was completely at a loss for words. I had never been spoken to like that in my whole life.