I have thought that for the longest time as well. It just seems it’s not coincidental that what happened to the jolly roger, who sent the note and where glinda comes in are the big mysteries kind of right now. I think it’s all linked!
Shipper-bias aside and just looking at it from Glinda’s perspective (if she did actually send the message, which I really think she did) the only vested interest she would have in Hook of all people would be his connection to Emma. Glinda, like most ~good characters, would have confidence in the power of TLK and the message specifically said that “the only hope was [Emma]” so she reached out to the other part of that equation, which would be Emma’s True Love
which is gonna be Hook but that goes without saying