Grelka. Light of my life. Fire of my loins. My sin, My soul. Why the hell won't you marry me?
According to some sources, Grelka is supposed to be available to the player as a potential spouse after the amulet of Mara has been acquired, but a bug prevents the dialogue option from opening, possibly due to a removed or bugged quest. This can be solved on the PC by targeting her in the console and using the command "addtofaction 19809 1", as well as the code "setrelationshiprank player 4 " which will open up the option for marriage. However, this is done at the player's own risk.
With 1.3 patch, the bug still needs fixing, but only typing "setrelationshiprank player 2" on her will do the trick.
This should enable the marriage dialogue options.
I've been scouring the internet trying to find out how to marry her - with no luck. other people are having the same issue. To give more details: Yes, the amulet is being used. Yes, it is a working version (I can ask my housecarl next to me to wed). Yes, we've completed ALL of the Mara quests. Completed most if not all Riften quests - including being Thane. I even completed the Dibella quest to become an Agent of Dibella which apparently "allows you to woo the opposite sex" Completed thieves guild. Nothing works. Even adding her via the console to the "marriage" faction - which works on other people, whos quests you haven't completed yet - fails to work. Most likely? It's either bugged, or they removed her as an option because she's a trainer and a vendor. Or they just removed her.
Possible leads: When searching for "Grelka" in the console, an item called "package for grelka" is revealed. I have not been able to find out where this item is, if there's a quest for it, etc. I think it's most likely left over files from when she WAS an option but nolonger is, since she doesn't give the quest. But, it's possible it's an item you find somewhere to give to her, I guess.
Hope this helps. Well, it doesn't, but maybe it'll save some time googling around.