I'm playing a new character to do some things differently than with my last one, and for some reason I don't get the dialog option to help Mjoll the Lioness find her sword. She is my favorite companion because of her unique dialog so it's irking me. I don't think there is a level requirement, so is there a way to fix this?

You can retrieve the sword without talking to her.

I believe you need to KNOW to ask her about it first, IOW, get the rumors and local scuttlebutt at the Bee and Barb first.

Grimsever can be found within Mzinchaleft before acquiring the related quest from Mjoll. This will open the quest dialogue with her, despite it having a high level requirement otherwise.

UESP

did you agree with her that the thieves guild was a blight to Riften and Skyrim? Or did you tell her you actually wanted to join the guild? She may not consider you a friend and talk to you about the sword if you sided with the guild.

I agreed with her. My other character is actually the guild master so i wanted some change. Where exactly is Mzinchaleft?

You must be at least level 14 to pursue this quest.

http://tamrielma.ps/skyrim/
Just put in the search bar of the place and it will locate it for you.

Or you just go to wiki/UESP and look at the minimap they provide you.

Ah, thank you