[Retroman]

Buy her a new boyfriend *budum tish* =]
Lol sorry, I couldn't resist...no offense intended of course.

Id narrow it down to:

Paris hilton or Katie Prices perfume, depending on who you think she likes more?

She's most likely got some decent straighteners? the majority of girls do at least. Plus it's too practical for a five month relationship, you need something more romantic.

Jewellery:

A heart shaped necklace locket with two small pictures of you both inside is always a good idea.

Or a bracelet with her name engraved on it?

If the name engraving is too pricey for you, or the pictures too much hassle, a nice regular necklace/bracelet would go down well.