Sorry to pour cold water on your partner's theory, but I'm pretty sure this has already been investigated, and no statistical correlation has ever been found between MS and allergies, although there is known to be a higher than expected familial aggregation (clustering in families) with certain other diseases, including Type 1 diabetes, rheumatoid arthritis, Crohn's disease, and Hodgkin's lymphoma.
It's also more common than chance alone would predict for individuals, as well as families, to have more than one of these diseases. So although they're all clearly different diseases, the evidence points to some underlying common factor. Not so with allergies.
In any case, if it was "common allergies", we'd expect the MS rate to be a lot higher than it is. It seems allergies are on the increase, with almost everyone claiming at least one these days. Why don't all these people get MS?
I'm sorry I can't point you to any scholarly articles - it's memory/laziness, not because they don't exist. If your partner is serious about her theory, I'm sure she'll take the trouble to research what's already been said about it.