Might it help to point out that both Princess Di and Kate Middleton got sapphires?
I think she'd be pleasantly surprised to hear how much of a non-issue it has been among friends, family, and acquiantances that me and my (also female) fiancee don't wear any engagement ring at all (our ruby and sapphire rings are both waiting to be resized).
That said, the point of a gift is to give something the recipient would enjoy -- not something you would want yourself. So, if it really makes a difference to her or her family, I'd recommend getting a diamond, even if it sets back your plans for a house, etc (I hope she understands that!!)
I think she'd be pleasantly surprised to hear how much of a non-issue it has been among friends, family, and acquiantances that me and my (also female) fiancee don't wear any engagement ring at all (our ruby and sapphire rings are both waiting to be resized).
That said, the point of a gift is to give something the recipient would enjoy -- not something you would want yourself. So, if it really makes a difference to her or her family, I'd recommend getting a diamond, even if it sets back your plans for a house, etc (I hope she understands that!!)