Her family and guests have been told they may even need permits to attend their own wedding.
Celé, from Killarney, Co Kerry, will be marrying Lawrence Mason on May 19 near Windsor, the same date as that of Meghan and Harry's nuptials.
The theatre nurse and architect never envisaged their choice of venue at the Tudor Barn in Burnham would conflict with that of the British royal wedding, but it's just 20 minutes away.
Some 100,000 people are expected to line the streets of Windsor in support of the royals, causing a potential security nightmare for anyone wishing to travel in the area during that time.
The couple became engaged in September, two months before Harry and Meghan, and never predicted any disruption.
A group of 12, including Celé's parents Stephen and Jeanne and four bridesmaids, will be travelling from Killarney to London for the big day. They have had to contact local police.
Mother-of-the-bride Jeanne told 'The Kerryman': "It is very stressful. My biggest fear is that Celé may have to wait for us and the guests to arrive.
"We will be travelling the same route [as the royals] and our predicament is that the roads will be closed. We weren't expecting this crowd around London for the day. The police are telling us that permits might be needed."