You did not provide a context. Both are grammatical English.
"She's one of them" simply refers to a group of identified people
"She's one of those" is an abbreviation for "She's one of those xxxx". For example,
"She's one of those (gymnasts)"
"She's one of those (brainy people)"
In a context where it is obvious what comes after "those" you can leave out the part in brackets.
Often these two expressions are interchangeable, so the short answer is they are usually the same.