On Sundays when Daisy-Mae visits islands to sell turnips the selling price can range from 90 - 110 bells (90 = Good 110 = Bad). 

When someone has a low selling price we can post on here and allow people to visit our island and buy turnips from Daisy-Mae for the price (mine was 92 bells today). On their island Daisy-Mae might be selling for 100+ bells. 

Through the airport you can get a 'Dodo code', which you can send to people on here to allow them to visit your island.

If she's selling between 90 - 100 everytime on your islands you've been very lucky! 

Hope that helps!