The recommended daily intake of protein is 0.8 grams per kilogram of body weight. 115lbs is 52kg, so 52 multiplied by 0.8 gives
41.6 grams of protein.
That figure should be sufficient, but there have been some suggestions that protein from plant(vegan) sources is less easily absorbed/extracted by the body, so maybe bump intake up by about 10% to account for this(although if you're using refined protein powders this may not apply.) Also, physically active people may do better with slightly more protein, say another 10% on top. So, taking these extra factors into account, 1 gram of protein per kilogram of body weight would mean
52 grams of protein for a 52kg/115lbs physically active vegan.
I agree with Drew_ab that getting protein on a vegan diet is generally not likely to be a problem.
Here's a more indepth examination of veganism and protein:
http://www.veganheal...rticles/protein