I hope I wasn't being nasty - I was just trying to say that in English spelling the letter o followed by ff - as in 'toffee' or 'coffee'- creates a particular sound: 'off'. If we've learned standard English spelling, that's how we decode it. Automatically.
Therefore, automatically, we read 'Soffee' as 'soff-ee' not 'sow-fee'. We then ask ourselves, 'Can that be right? ' We have, separately, learned the widely-used proper nouns 'Sophie' and 'Sofie'. We read them as 'sow-fee'. But the unusual 'Soffee' = 'Sophie' does not fit this pattern. So we feel puzzled or irritated or confused.
Of course, if we meet little Soffee every day at school or in the park or at playgroup, and are told by OP or another how they would like us to say her name, then we soon learn it, just like we learn any proper noun, and it stops being a problem. But for the countless other people who Soffee might meet during her lifetime - either for the first time face to face, or through the medium of written language (forms, computers etc) the puzzlement reaction is likely to occur with each fresh encounter, and may not be nice for her.
However, it's entirely up to the OP whether she thinks all this matters.