Be consistent!
Take her out often.
If you catch her in the act, interrupt her (clap, make a loud noise) then take her directly outside, even if she already finished in the house. (don't punish her)
Buy a "pee stick"
Simple Solution Pee Spot Pheromone Stick | NextDayPets.com
Reward her every time she goes outside (verbally, with treats or a toy, whatever she responds to.) at first, you don't have to do this forever.
Buy some Nature's Miracle and use it to clean up any messes she makes. She's more likely to go inside if she smells her previous messes and regular cleaning supplies won't get rid of all the scent.
If that doesn't work and there's one place she always goes, leave something (paper, puppy pad.. whatever, but always use the same thing, every time) to mark the area, then start taking that outside with you and try to get her to pee on it there.
Good Luck!