How much ukemi training do you have in your dojo? I've been in the same position at a seminar. I asked the her(in this case) how much ukemi she had trained. She told me that they didn't teach that, you had to learn it the hard way. After that session I asked her if she would be interested in some ukemitraining, and she agreed. I did the basic with her, I mean from seiza doing a roll forward, and sitting on your but doing a roll backwards. Soon we did it from standing and she build more confidence ( It didn't hurt her!).
The next session she had no problem being uke (she told them she didn't do breakfall) and she thanked me after.
Nicola, even if you have ukemi training in your dojo, do more, maby as a warm up! If she start to feel she can do both break fall and rolles then maby she'll not be afraid anymore. I do not believe ignoreing her is the right attitude in a dojo.
'Hope this is of some value!
Train with a smile on your face, and your Aikido will be circular and without corners.