Hi, I had a similar problemi with a girl for her birthday. We were in 6 persons and had to decide between S3-like device or S3 mini-like device. The problem was dimensions. Commonly girls are not geek so they will not search for mods, new roms etc and they are not obsessed by performance. So we decided to choose a phone based to confort, easiness and look. We had tested reactions of some other girl by but some device in hand and asked HOW they feel about. Majority had said that have a small device (like 3.6"-4") is confortable in hand BUT it's not easy to write on the touchscreen. A note-like phone is too big and for a girl but we had tried to understand. Something between is S3-S4..."it's not small but it can feet in my handbag and it's confortable when I must write" This was our goal. So we had bought an S3 for a price reason, and she is now a happy android user.
My advice is to buy a phone that is not a note-like and not small that ZR. Another thing, my sister have the ZR and she say that it's ok =)