I tend to say Miss unless I see a wedding ring, Ms sounds sooo pretentious (to me) & if she turns out to be married it's unlikely she'd find Miss an insulting term, she'd probably just correct you without really thinking too much into it.
i say the first name and the surname. I often have to ring people up for my job and if i dont know if they are married, ill say "can i speak to eg, lisa clarke please"