Knee-Jerk Reaction Nipping

My 16-month-old Mini Aussie is maturing and learning self-control. Some anxiety issues are diminishing and she is less vocal - yay. However, we still have an issue regarding nipping. Actually, I think these may be two separately-caused issues.

1) She will often sleep at our feet or under the table while friends are visiting. If she is asleep or zoned out and someone accidentally nudges her with their foot, she swiftly nips the foot (front teeth, no canines, but a heck of a pinch). It is lightning-fast like a snake bite and it appears that even she is surprised by her action. She seems to show a bit of remorse immediately following the event. The short-term solution is obvious - don't let her lie down under the table and/or say her name before moving. But, how can we train her out of this behavior?

2) Secondly, she is very cautious around strangers or anyone she doesn't know well. As we try to socialize her, she sometimes decides that the person has invaded her space bubble and will react with a nip. In a couple of extreme cases, she pulled back after the nip, but her mouth kept nipping (like someone with chattering teeth) until I calmed her down.

Any tips? (Please tell me she is going through a phase that she will grow out of in weeks. :) ). I'm concerned. I don't want her to hurt anyone. And, I want her to be a happy, well-adjusted dog.

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