But Pinky, what is to stop people pronouncing Siobhan See-ob-han or Niamh Ny-am or 'Nee-am', or Sinead 'Sin-eed', or Mairead 'May-reed', or Aoife 'Aa-oh-ih-feh'? As Stoirin says, it gets confusing if everyone can just make up their own pronunciation or have a stab at it based on the conventions of a different language.
Could I pronounce George 'Ge-or-ge' with hard Gs (same for Georgia, Georgina, Georgette?)
The names are actual names with a way of pronouncing them that is correct and based on the spelling and pronunciation rules of the language they originate in (with regional distinctions obviously just as you would find different regional accents in Britain). It is disrespectful of that language to proceed on the basis that any convenient pronunciation will do.
There are Irish names that have Anglicised spellings, like Maeve for instance, that are acceptable. In Irish Maeve would be spelled Maedhbh, or Maebh for a more modern version. All are pronounced the same. If you want to pronounce the name Sorcha 'Sorsha' then I would spell it like that, S-o-r-s-h-a.
According to Irish spelling and pronunciation rules, Sorsha would be phonetically spelled Sóirsea. If you are going to keep the Irish spelling but pronounce it differently you might as well write her name as 'Evelyn'?