Sounds like hypocrisy to me, however you want to rationalize it. President Assad is no Saddam. Saddam killed millions, most with poison gas (a definite war crime). Yet we were still prepared to negotiate with him. If you don't know what advantage we'd gain from talking to Syria I'd suggest you should read the Baker-Hamilton plan.
Besides, Ms Pelosi made a fact finding trip, not a diplomatic visit. Also, there's not much to undermine since the President, and not Congress, controls the State department and is therefore responsible for diplomatic relations with other countries, or the lack thereof.