This issue goes to the heart of giving and receiving gifts.
When you give a gift are you giving also a burden that the receiver must keep the gift forever? Or for a certain period of time? How long?
Is it really in the spirit of giving to give a burden/obligation to another person?
If not then it is their's to do what they want with? It was given after all.
Maybe they have 2. If she is selling it as new her DC probably hasn't played with it. As heartfelt your gift might have been when you gave it, it was essentially unwanted. This is part of the reality of giving gifts. Sorry if that makes you feel bad - I'm sure your friends isn't trying to make you feel bad - as others said she might be skint. Or she might be trying to release her family of the burden of all the stuff they have.
We have limited space in our homes, and we are surrounded by the 'normality' of giving stuff to other people. It seems much of our society is fuelled by their. Much of these gifts, I would argue and ever increasing percentage of it, is unwanted.
I've dissuaded my friends and family from giving me gifts for years, and usually they ask what the DC might want or need. Half of MN will now pile in and tell me how rude and ungrateful I am, and I don't care.
I don't have room for the stuff we have - incoming stuff is a problem.
I try to give experiences, or time, or consumable gifts from homemade biscuits and sweets to iTunes vouchers. Things that can be used and remembered and shared. Things that don't take up physical space.
It can be a challenge but unless I know someone specifically wants or needs something then I don't give it. I consider much gift giving as junk circulation.