That would be a technical breach of the immigration rules, which could cause serious problems for any future visa applications she would choose to make. If she wishes to visit for the purposes of marrying you and then returning home then she would have to apply for a marriage visitor's visa (as opposed to a simple visitor's visa) as you will see from this link:-
See " Visiting for other reasons" at the bottom of the page.
If what you would like to happen is for her to come to the UK to marry you and then settle permanently with you then you need to make a completely different application.
I can provide you with guidance on this if you wish but you would have to submit another question to the board because it's a separate issue to this one (ie. a visitor's visa) If you wish to do this simply submit a further question and request me via my profile and mark yoru question "FAO Tom".
Trust this clarifies, please click accept.
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