until not so long ago it wasn't that uncommon for babies of single parents to be adopted by their grandparents/aunts etc.
My dad's youngest brother is actually his sister's eldest child who was adopted by my nan, similarly I was at school with a girl who had been adopted by her grandmother. In both these instances the families are still close and neither of the birth mothers have had issues being close to their children yet not having a mother-child relationship with them.
While of course some parents do change their mind I think it's important not to assume that this woman will change her mind based purely on our own views. After all most commenting on this thread have our own children and therefore the concept of handing over one of them to be adopted is inconceivable to most of us. Many, many women give up babies for adoption every year for many reasons, and for a lot of those women it is the best thing for them and their baby, and they do so without regret.
In the US open adoption is quite common where birth parents and adoptive parents form a relationship before the baby is actually born and those parents do keep in touch after the adoption has taken place. So I don't necessarily think that if you were to adopt your friend's baby it would signify the end of the friendship.
First and foremost I think your friend would benefit from some counselling to help her come to terms with the situation she has found herself in, and to decide what she really wants to do. If she really does want to give the baby up for adoption, and you really feel that you could adopt this baby, then you can consider the longer term prospects, but obviously you'll need to keep in mind that your friend may change her mind once the baby is born, and this is something you would need to make her aware of - that you will accept what ever decision she makes. After all, your friend doesn't need to feel pressured into giving up her baby because she knows how desparately you want one, iyswim?
If I was giving a baby up for adoption, I would rather give it to a friend who I knew would take care of it, and love it, where I knew I would be able to know how it was doing, than giving it away to strangers and never having the chance to see it again. Similarly if I had a friend in this situation I would rather be the one to adopt the baby than see it be taken off to who knows where.
Good luck.