medications work differently for different people - a medication that works really well for me may not work for your friend. That means that when you're looking at injection versus infusion, you look at some of the other factors. For instance, infusion drugs have to be administered in a clinic/hospital setting once a month or every six weeks and you spend a good portion of the day getting the infusion.  Injections are given more frequently, once every two weeks or so, but it's something you can do at home yourself and takes about five minutes.  Your friend has to ask herself which works better for her lifestyle and temperament - for instance, some people really don't like the idea of injecting themselves, but once you're used to it, it's very easy.  Personally, I would choose injection drugs because I prefer to to have very little medical stuff in my life - the less I have to go to a clinic or hospital, the better, but your friend may feel differently.

That said, your friend should have a conversation with her rheumatologist about what they recommend - they may feel that one particular drug is better than another, although as far as I can tell, there is no way of identifying which drug will work better for  you.