Congratulations on adding Argie Sweet Tooth to your collection, she is a gem.
If you want to keep her as original as possible, don't rehair her
The Nirvana hair is often unique in colour and texture, so it can be hard to find a match. You are correct, "Sugar Berry" is the best/closest match to Argie Sweet Tooth's colour. If you do decide to rehair her using vintage hair would be best, sometimes new nylon can look a little jarring on a vintage pony
Love pkw xxx