Yes, in this day and age "Deutsch" would probably be written "ドイッチュ" or "ドイッシュ", and "sweater" would certainly be "スエーター". But "Doitsu" and "seetaa" are idiosyncratic because they're very old loanwords adopted into Japanese before there was a standard pattern of transliteration. Current common practice is a lot more standardized and in most cases completely predictable. I'm not saying there's not room for interesting interpretation of character names (and quite honestly I don't even like the name Sherrill much); but in this particular case, because Hoshino went out of her way to include the little ェ e and create the foreign-to-Japanese sound シェ sheh instead of using the natively-Japanese セ se, I personally conclude that the "sh" sound was specifically intended. </blah blah>

Haha, personally I mostly use the pre-localization spellings for everybody. I've grown too attached to "Rabi" and "Linali" and it's always seemed a shame to me to obscure the reason behind all the rabbit jokes with "Lavi".