Tamsin is pretty enough; where I live, it's dated to the 1970s, and it seems too nicknamey to me, but it's certainly OK.
I was at school with - off the top of my head -
Allison Adair,
Barbara Bam,
Cheryl Clark,
Deborah Davis,
Mary Mitchell and probably many more. None of them had a moment's trouble, to my knowledge. I also knew a
Johnny Johnson who raised no eyebrows either.