Greeting a Muslimah?

As-Salamu 'Alaykum -

Today I went grocery shopping, and while I was in the store I turned around to see a Muslim sister walking past- the hijab was what tipped me off. As I was wearing my kufi, I'm sure she must have seen me as well.

Now, as soon as I saw her I instinctively greeted her with "As-Salamu 'Alaykum" as I do with the sisters I know at my masjid. She turned to me with that deer-in-the-headlights look and returned my greeting and kept walking.

Now as I thought about her reaction it occurred to me that one of four things might have happened:

A) She was simply startled;

B) She was surprised that a stranger had a kind word for her;

C) I committed a breach of etiquette by speaking to her without her having a male companion present; or

D) All the above.

Being from the South, I'm used to greeting people even when I've never seen them before, but since becoming a Muslim I'm still learning the ropes about proper etiquette- did I make an error in speaking first, or speaking at all?