Her frustration could have been due to any number of things other than jealousy. She could have been wanting to spend alone time with her friend and was frustrated that you kept the conversation going, she could have been late and wanted to get somewhere, she could have sensed her friend was uncomfortable, she could have been in a bad mood— anything. Jumping to the conclusion that she was jealous seems like a stretch. I would simply proceed based on whether or not there is mutual interest.
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