Don't know what show you saw but Tabitha St Germain did a incredible job as Shana and many believe she did better then Rie Kugimiya did. The one thing people complain about is that Shana sounds very different compared to the Japanese but that doesn't mean bad. The English version is a completely different take that works just as well(In my opinion better because she doesn't sound like a child and instead sounds like a real person with real issues in her life). While I would 100% agree with you that Carrie Savage could do the character well I would not want to see that happen. Reason for this is I found it refreshing that Shana didn't sound like a child and instead sounded older then she looked. However if Carrie Savage was cast she would end up being told to play Shana like she did Rihoko in Witchblade and I really would not like that(Despite her performance in Witchblade being incredible along with many of the other awesome things she has done like Rumbling Hearts) Again I and many others liked the performance Tabitha St Germain did for Shana and a good reason for it is because it's different. It still stays true to the character without trying to sound exactly like the Japanese and very few dubs can pull that off.
The rest of the cast can be debated a bit more heavily as there were some characters that didn't do all that well(although many of them are very minor characters) and others that were mis cast however by and large the dub was very very solid. I would not say it's oceans best dub(That honor would go to Black Lagoon) but it's easily a excellent one. I mean fans will say when they don't like a dub(no one complained about the re dub of Initial D for example as it was terrible) but pretty much every fan of Shana wants the original cast back and there is a solid reason for that. I do think that if they had to Funi could make a incredible dub for Shana but I doubt they would be able to capture that certain something the original did.
EDIT: In regards to the way Wilhelmina talked. She had a very odd way of talking in Japanese that would not translate if done directly so instead they added on the word Indeed quite often to make it seem as though she had a odd way of talking. Some people hated this some loved it. I thought it was entertaining but I can see if it annoyed you.
As for the spell and pronouncing of the name. This can easily be linked to the Japanese. As many know in Spice and Wolf they called Holo Horo even though the name is spelled and said with L's and no R's(many fans didn't know this and complained about it being Holo in the dub despite it being the way it's supposed to be said) There was also the famous thing about Alucard from Hellsing in which the Japanese studio insisted about Arucard when the name is obviously supposed to be Draclua spelled backwards. The issue regarding the name could have easily been something similar in Shana. While I don't know for sure that's the case the fact that we are talking about R and L here is a very good indication that this was the case and the Japanese made the dub happen the way it did.(This was the case with Hellsings subs. The Japanese made them put the Arucard in the subs while allowing them to say Alucard in the dub)