The "risk" here would depend on how severe the build-up has become. Is it currently blocking her vent and impeding the passage of waste or is it just a bit of crusty gunk mucking up the feathers back there? Some birds are messier than others, it can also have to do with the consistency and quality of the waste they are passing as some will pass more cleanly than other. Cleaning it up is a great first step, and it may correct the matter as getting rid of all the build up removes the 'platform' for further build up - if, though, it starts to build back up again you may want/need to work towards other corrective steps such as trimming, adjustment in her health, etc - or just keep on top of the clean-up back there to keep it from getting bad again.