Marriage is a tricky, and rather touchy feature of Skyrim to start.

Proper Wedding Ceremony

You have to be careful with the wedding ceremony.

The priest will tell you the ceremony takes place the next day between dawn and dusk, which is 8 AM - 8 PM. If you arrange a marriage after 8 PM and before 8 AM the next morning, you must enter the temple between 8 AM and 8 PM. If you're inside, the marriage won't start.

If you arrange a wedding after midnight do not wait a full day until 8 AM, you will miss the ceremony and fail the quest. It's a good idea to make a save before you propose to someone, so you can retry if you encounter a mishap.

Disable Mods

If you have any mod(s) applied to your game, you can temporarily disable them and see if that's a fix, as modifications to the game add extra headache for the scripts to process, and can make problems worse.

Using Console Commands (PC)

Also, depending on your system, you could use console commands to force her to marry you. If you're using the PC version of Skyrim, you can preform console commands.

1. Open the console tab with the "~" key.
2. Click the NPC you want to marry.
3. Type "addtofaction 19809 1
4. Press the "Enter" key.

You should now be married to whomever you wish.

Load a Save Prior to Proposal (Xbox)

Assuming you're on the Xbox however, the best option if no fix can be found, is to load back to a save prior to the proposal of whomever you wanted to marry, and either retrying, or picking a different marriage candidate.

Well, 1st off, you have to make sure you have a house. Before you propose to someone mame sure you save the game. You also have to be there at 8 am or 8 pm (before dawn and dusk). This glitch can happen sometimes so also before you ask marmal to arrange a wedding save your game again. Also there is another glitch where the person your getting married to says "where should we live" and then leaves the temple. Thats why you should save the game before you ask marmal to set up the wedding. ?

First off, you do not have to be there before 8 AM or 8 PM. You can go anytime to the Temple of Mara and set a time with Maramal to marry you to your favorite NPC. He will give you 24 hours before you have to be there for your wedding to start. After that, you are in the soup like the rest of us fools. Remember the honeymoon does not last forever.

Also, I believe the information in this answer will not allow you to get married to anyone. If you use the console commands: setrelationshiprank player 4, the NPC you want will like you. If you add: addfac_19809_1, then the NPC will love you. But none of what is stated in that answer will allow you to get married. It has to work through Maramal or it will not work at all.