The time to make any big revelations is now - while the relationship is still young and sexy and hot. The trick is to work out how to tell her and this can be difficult because, basically, you are risking your whole relationship here and someone you feel comfortable enough to share this with is not someone you want to lose because they go 'ugh!'

I think you started well with the game but you need to follow up. Maybe you should offer to treat her to a 'nice evening'. Start with dinner etc, you both dress up nice, flirt etc. Plan for some things in advance but keep your plans hidden until the last minute. Start small (maybe get hot and heavy over dinner and suggest you just do it there on the kitchen/dining room floor?) and work up in small increments - perhaps a bit of bondage (have your cuffs nearby for easy access), some pain (perhaps gently bite her nipples or ask her to bite yours depending on your preference) and see how she reacts to each step. Basically take it slow and careful and make sure you judge each reaction and quickly back track if she goes 'Ugh! Thats really horrible!' If she seems to enjoy it, try a little more and so on. Be prepared to back pedal if it does not seem to go well and try something else.

Keep up these regular 'experimentation' sessions (maybe once a week) for as long as you need to. Maybe vary the setting (a different room but always make it nice for her - possibly use set dressing, lighting, scents etc) and what you do - both in sort of actions and intensity. By the end of a few weeks you should have learnt a lot about what she likes and doesn't like and maybe be a bit more confident about what you can and can't ask her to take part in.