It's +4 for fair trade and +1 liberation if you can settle close enough to her capital (I don't remember the exact details, maybe it needs to be closer to her capital than to any other capital?). So it will get her to pleased which allows begging (at cautious you are threatening her). Since you have currency, beg for say 10.Until you mentioned it earlier in this thread, gifting a city had never occurred to me. Will it really keep her off my back for a significant amount of time? (I really don't know anything about how diplo works).
10 is plenty, though you might want some more at IW.I only have 10 workers. Building more is on my radar, but until I know what I'm going to with them...