Excess weight is one of the leading causes of knee pain, but as a female there is another issue to examine: Q-angle.
Quick overview: http://sportsmedicine.about.com/od/women/a/Q_angle.htm
More in-depth: http://www.aafp.org/afp/991101ap/2012.html
Before deciding on stretches to ease the pain, it is important to have an accurate diagnosis - a consultation with a physiotherapist would be ideal.
Some of the more common sources of inner / front knee pain include:
Click on the above link for detailed information about these conditions including appropriate treatment.
You might also be interested in checking out the following knee flexibility exercises:
Hope that helps and good luck,