Things one may or may not know about Grell. All of this was eloquently composed by the mun of
esoteric_rose. Most applies to both our interpretations for Grell. There will be blatant notes at the bottom where my characterization for her differentiates. I'm putting this up because her brilliance should be known, and this is a good reference for myself as well.
She does not want to flirt with any man about her. Sebastian is attractive, yes, but she certainly has some form of standards (see Ronald in the recent arc). She is also not inept. This is a person who managed to pull off the greatest unsolved serial killing of all time.
Romeo and Juliet is not the only Shakespeare play she would know-what the play reference shows is that she's got a literary bent.
She would not threaten to kill someone mildly[1], though she is morbid, she views death as (nigh?) sacred (see how the reapers react to the Bizarre Dolls/zombies) and thus, death threats would be serious.
Yes, she can be silly. No, she is not supposed to be comic relief-I repeat, she was a serial killer.
So many people, myself included at times, though I'm working on it[2], forget that she is deadly and messed up as hell.
Going back to romance: the excessive flirting around Sebastian? Seems a bit more like a battle tactic than her actual way of flirting. He got confused and disgusted, she was able to get in close and hurt him.
And she does seem like the type to take real romance seriously, if you believe that she honestly fell in love with Ann, she broke one of the highest laws of her kind to help her out, so romance is not a trivial thing. Something to be bandied about, but nothing emphemeral[3].
Oh yes, and she's not weak. Yana herself said that Grell's stronger than anyone else in the series aside from Sebastian, so if she wants to lay down major damage she can. She can protect herself just fine.
[This part is my own notes] Children are a dream Grell would like to have come true. She does not like most annoying brats, but if she were to raise her own, it would be a different story. She would want that child to have a life she could never have: a happy one. No one is mother of the millennia, but Grell will surely try.
Notes:
[1] No, she will threaten to kill you if you cross her to such a point. She would do it elegantly, and make it seem as if it were just a puff of dark smoke. Harmless, as smoke can be from a distance, but can be deadly if left wafting through the air in stacks. Most do not cross such a line, thus, most think Grell is full of hot air. That notion is partially true.
[2] This doesn't apply to me. I know Grell is a crazy bitch. And that's what I love about her.
[3] I don't necessarily agree Grell was in love with Ann, but perhaps there is a sort of deep kinship between them. I do believe that Grell cared for Ann in a plutonic way. Although it should be kept in mind that the backgrounds for
redcinemareel and
esoteric_rose are different, and will play a part in how they would care for Ann.