Yes, the realtor had an obligation to tell you this IF she knew (she does not have to do indpendent research, but can rely on what the seller tells her; she is not responsible if she was not told about the right of way), though it should also have come up during your title search.The seller also had an obligation to disclose this, since it is a material condition affecting the sale. Speak with a real estate attorney: it is possible that you could, if the right of way is a serious enough impediment to the use of the property, use this as grounds to void, or undo, the sale; otherwise, you may be entitled to monetary compensation. You may have a claim agains the seller and/or the realtor.