Dear Swapna,
As per your post, i clearly understand that the person who kept the gift on the table want to impress her for his own. After a weeks time she is escalating this to you, its better to get the written complaint or in the mail and with the compalint. You can check the CCTV records for the person who kept the gift on her table don't take to the mgmt for this simple issue.Give warning to the concern person and get the written statement from him that he won't do the same in the office premises. Tell him politely and explain it clearly its not the place for these types of activity and also tell the girl that henceforth these type of activity won't repeat and ask her to bring to notice prior.
Regards,
Gowrishankar.G