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She is senior than me and she is working in a good department also.
This fact doesn't matter. Keep this in mind.
Next time you see her, grab her by the arms and tell her that you need to discuss something important now near the coffee machine! No more explanations than this.
When you are at the coffeemachine, tell a great story about you showing DHV, humor, some negs . At the end of the story, you take her by the arm and bring her back. And just say: 'that is all. thank you!"
She will be flabbergasted and will wonder the whole day what was going on. Probably she will come back to you and ask you what is was all about. And you say' You seem like a nice person with sense of humour and I just needed to tell someone this story'. Wait her response...and then you say (no matter what her response is): you know what, since you are a good sport today, let me buy you a decent coffee.
The rest is up to you