You might want to consult a couple more Realtors on the market value of your home. Most of the estimates should be in the same ballpark.
It could be that your friend is being more honest with you about the value of your home and the other Realtor gave you a higher number because he already knew you expected it. This is called "Buying a Listing" and is the subject of an article on our web site.
Or it could simply be that your friend is a good friend, but not that great of a real estate agent.
Mixing business and friendships is always risky to the friendship. On the other hand, if your friend is truly competent and was providing wise advice, she may be offended if you ignore the advice and choose another agent.