I had always read that Sagitarius and aquarius were bad matches . . .. here is something less wistful from one site:
Since Aquarius is disenchanted with the weaker types of the signs and finds Sagittarius, who oozes strength, he/she will at first believe this to be a perfect mate. Sagittarius may have been searching for someone who would be able to live the kind of free and easy life style that he/she enjoys and at first sight, which will probably be at a social function, Sagittarius falls for Aquarius in a big way.
Sagittarius approves of the Aquarians constant involvement with the world and fails to realize that while Sagittarius is living life in a carefree way and can come home at night in a light hearted mood, Aquarius cannot do this. Aquarius is too busy trying to cure all the ills of the world, help the down and out, and generally be at the beck and call of others no matter what time of day or night, others except Sagittarius, who will be left alone to use that inner strength Aquarius fancies he/she to have.
Sagittarius, being a much more hot blooded person than Aquarius and free from most sexual inhibitions, may find the bedroom becoming the battle ground especially when Aquarius is not as responsive as Sagittarius would like and eventually Sagittarius will seek satisfaction elsewhere. This is not a match made in Heaven.
you should break it off with her and use this as an excuse . . since she seems to find astrology relevant . . . hmm . . thats a great break up excuse 