acostaroad - I was in this exact situation. I was widowed at 26 after having been married (sealed in the temple) for only a short time. We had no children. At the time I was devastated and wholly devoted to my deceased husband. I thought I would live my life single and just "wait" till we were reunited. Over time, I healed and the Lord brought a wonderful man into my life. We were sealed in the temple shortly before our 1st child was born. I had to request special permission for the first sealing to be cancelled so that I could be sealed to my 2nd husband. That IS something the church allows for and I'm sure it is done on an individual basis and is not openly discussed out of reverence.
It is entirely up to this girl to choose what to do when the time comes. She is not "stuck" because she was sealed to someone who is now deceased. The Lord knows that circumstances change and He allows for that.
