In reply to blanchie14c:
I would take Mrs B to your local Bravissimo store and get her checked out for size first. The ladies there are really good and can recommend a range of bras and suggested sizes for her. I went for a fitting at Debenhams and was sized at a 36D, a trip to Bravissimo sized me at 32FF, which not only put a smile on my face, but also provided a greatly better fitting bra.
Unfortunately my experience so far is that there is a limited choice of bras available for the lady with anything larger than a 'C' cup, and once you get into an activity with more movement than a sedate yoga class, you can really struggle to find something which offers good support.
I can recommend Pure Lime sports bras. I can't remember the exact model i have, but it offers good general support and is comfortable. I've also just acquired some Odlo bras, they are not very supportive but are comfortable and I like the look of them.
If Mrs B does any running, I would highly recommend the Shockabsorber Run bra. I really struggled with running as my chest just did not seem suited to it. The 'Run' bra holds them rock solid and is brilliant. I do use it for other activities, but it can be quite uncomfortable when you wear it all day.
hope this helps