I re-read New Spring too ... Gitara's strength is never directly mentioned, but there are a few hints that she may have been one of the women between Cadsuane and Moiraine in strength.

Her age being the top of the list. She is supposedly over 300 which would require significant strength in the OP.

Secondly her influence. She is recalled as the Andoran advisor to be Keeper. Of note here is that after Gitara's tenure as Advisor the next woman to hold the job was at the highest rink of current AS strength .. Elaida.

Third ... Cadsuane doesn't speak of her strength because she's already dead, but she was most likely to as strong as Mylene or Karene given Cadsuane's comments, but in the same breath Cadsuane notes that there sold be many women strong than Moiraine