Yes it should be safe for her as long as she doesn't combine the two. If she can spend the day without taking ritalin that would be safer and probably a nice, cleaner MDMA experience. Since you say she's been taking it for years I'd guess that she may not react well to a day without it? If that is the case it wouldn't be the end of the world to combine the two but the risks are higher. Combining two stimulants causes far higher body stimulation (sweating, gurning, heart rate & blood pressure increases) than either would alone at equivalent doses. Being over stimulated can also cause a lot of anxiety. As a result you'd definitely want to keep the MDMA dose low in those situations which it sounds like you are planning on anyway.
