Here is a link I found on peripheral edema. That is the name for the swelling in your mom's legs. On the web page it states that there are lots of reasons for leg swelling. But the things I noticed which may be relevant to your mother are age and steroids. I know you said she was getting infusions. But you didn't say what the medication was. So I just guess it might be steroids. Since we MSers get those sometimes.

Here is the link. I hope you can find some good information here. And I hope your mom is doing well.

http://www.umm.edu/ency/article/003104.htm