Anne was born between 1501 and 1507, though the general consensus is around 1501/1502. So if we get a Princess Mary around the same time, if only a year or two later, then it would make sense for Anne Boleyn, a lady of good name and great connections, to act as a playmate and maid of honour to the Princess.
The idea that Arthur might seek to use that bring allies into to help reclaim some territories in France isn't ridiculous. But it will most likely be as effective as Henry was OTL and would most likely happen around the same time. Actually, I can see Arthur pulling most of Henry's early stunts to some degree. The only difference would be that the Duke of York, instead of the Queen, would act as regent during these times and he may be more or less successful depending on outside factors.
Interesting, and with the Boleyns at court, who knows what schemes might arise eh?
And interesting, what makes you say that it would be Henry as regent? Would Arthur not want his brother by his side?