How can you tell the reason?

I know when a girl asks if you have a girlfriend/are single there are 3 possibilities. She's either interested, has a friend who may be interested, or is just curious/making small talk. Is there a way to determine what her reason could be? Like I was talking to a girl (she's a coworker), she just said how these two people were together. I said oh, cool, etc. She then asked me randomly in a curious/interested tone if I had a girlfriend. I said no, and she said why. She then asked me about my past relationships/if I had been married before and all. A few days later she brought it up randomly, asking why I don't want/get a girlfriend. I don't know her that well, we just started working together a month ago, and I've done nothing to show interest to her. When we talk it's usually first about work but the conversation often goes to small talk/personal stuff, which she likes continuing (unless she's really busy with work). She also does often send me somewhat flirty emojis (smiling face with three hearts one, the pink heart with sparkles one). A lot of them are just sent by themselves. And the talk is casual, like if I just say thanks/no problem/I'm coming/etc. I didn't think much of them, as that can be done in a friendly way, but now I'm not sure.

How can you tell the reason?
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