Multiple Sclerosis is frustrating disease because they're not sure what exactly causes it. There are possible genetic links, but nothing concrete or obvious enough to say it causes MS. However, it is NOT contagious and I believe it is technically classified as an autoimmune disease. Which means her body is fighting itself in the same way a body would fight against an infection. Therefore the only thing you can get from unprotected sex with her is an STD (if she has one), or a pregnancy. If you guys do consider having children, please consult a OB first, as her MS may complicated a pregnancy or put her in a high risk group.
http://www.msaustralia.org.au/aboutms-faq.asp
This is a pretty clean cut question and answer page for MS that may help you.
you cant catch ms from unprotected sex its a genetic disorder x