Would it be offensive for my daughter to give her friend a Star of David necklace for her Bat Mitzvah? We are not Jewish but my daughter wants to recognize her friend in a meaningful way. Thank you.
A star of David necklace is not a ritual object (just pretty jewelry), and I've never seen anybody take offense at one being given by a non-Jew. This is, in fact, one of the safest Jewish items you can buy; were you to try to select books or ritual objects, you would quickly run into matters of differences in tradition and would risk getting the "wrong" ones. (Also, family members are likely to give ritual objects.)
I've seen the Orthodox proprietor of a Judaica shop gently question a customer who seemed unfamiliar with Jewish objects and who was shopping for a mezuzah, but I've never seen people shopping for jewelry be questioned. That's anecdotal and limited (I don't spend a lot of time in that shop), but I'll include it anyway.