The 26-year-old has chosen two wedding gowns after commissioning Karl Lagerfeld to design the frocks at a cost of €43,038.
The Smile hitmaker even forked out an additional €6,795 on flights to and from Paris for fittings with Karl at his HQ.
Allen, who is marrying Sam Cooper on June 11, apparently spent less than 24 hours in Dubai on Wednesday for a launch of her fashion collection Lucy In Disguise before she headed to the French capital for a final fitting.
An insider told British newspaper the Daily Mirror: 'Lily has been planning her dream dress for months and couldn't decide between a classic, full-length ivory and lace gown or a shorter, more modern dress.
'In the end, Karl suggested she get one of each and decide on the morning which she’ll wear down the aisle.
'At the moment it looks as though she will plump for the more classic, vintage gown with a small train for the ceremony, and then change straight after the service into a shorter, tighter number.
'The latter will be more in keeping for the evening party and will allow her to dance more freely.'
The source added: 'After rocking up in Dubai earlier in the week, Lily had to fork out extra for an unscheduled flight back via Paris to meet personally with Karl at Chanel.
'Having your dresses tailor-made in France isn't the most practical of ideas but Lily is certainly thrilled with the end results.
'She believes it is been worth every penny and every air mile.'
Lily will reportedly be changing her surname to Cooper after the couple get married.