Marriage visa application before marriage ceremony

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Dear Immigraton experts,

My partner is currently on healthcare visa and we plan to get married soon, however her visa runs out 3 days before the date we have been given for marriage ceremony and that is the earliest available date for the ceremony. We have been told she can look for other venues which may have earlier dates, however that will mean another 28 day notice to the home office so we decided to go with the date given by our local registry.

My question is, since she has to apply for the marriage visa before her current leave expires, can she make the spouse visa application and then send the marriage certificate later when we have received it after about two weeks after the marriage ceremony? We have been told that the marriage certificate takes about two weeks to arrive by post after the marriage ceremony, by which time her current leave to remain would have expired.