Hi Leslie,
It CAN BE a problem, but not in the way you think.
EFT doesn't really address negative energy. There's just energy that is flowing and energy that is stuck. If stuck, or blocked, it causes damage, pain, psychological, or physical. If flowing, one is healthy. Of course, there may be some areas or aspects in which energy is flowing and others in which energy is stuck. The stuck energy is stuck because of one's thoughts and beliefs. Even if a trauma happened, and that caused a person's energy to be stuck, it's more to do with the way the person processed the trauma in his brain and thinking, than the direct results of the trauma. That's why you can have individuals who may have missing limbs, or serious illnesses, but they are very healthy in that their energy is flowing. Perhaps their illness was caused by a time in the past when their energy wasn't flowing, or perhaps it's just the best thing for the person. In EFT one doesn't usually say "physical health is good, physical disability is bad". Either of these can be good, or bad. Whether one does EFT for a physical issue or doesn't depends on how much the person is disturbed by their situation, which indicates how their thinking is out of sync with reality. When doing EFT, sometimes the physical issues are resolved, and sometimes the brain patterns are resolved. We are not Healers, for we can't create Physical health, however, we do try to be healers who help others have Emotional Health, and the physical health or solutions to support that. Emotional Health is often in our power - although for many, it is a long journey indeed - while physical health is not in human hands alone.
Having said all that, beliefs are infectious! So if you do EFT for a friend with a negative mindset, and you don't know how to address their thoughts with EFT, then you might absorb some of their negative beliefs. At this point, you can choose to live in turmoil :-) or you can EFT the conflict you feel. It can be very liberating to learn about others' beliefs. Even if it causes inner conflict. Because that way you grow.
Many of us have enough inner conflicts already, and we would prefer to work with more of our own issues first, because it seems gentler. But if you feel drawn to work with her issues, then perhaps it's part of your learning curve. The question of absorbing her negative beliefs will arise if she is very angry, or doesn't trust you, or EFT, or doesn't want you discussing her private beliefs and lifestyle or thoughts. So basically, if you are very non-intrusive in your offer, and don't insist that you EFT help is something that she NEEDS, then she might choose to take you up on it, and it may be a wonderful healing experience for both of you. While if there isn't trust, either in you, or in EFT being helpful, or if she has no intention of tackling any of her beliefs in order to alleviate her pains, then you might be disappointed. Which might activate all sorts of negative thoughts in you that you never knew about, and you'll have to deal with them! That's the sort of negative energy that gets transmitted. Either because the two of you have different goals, or because one of you is pushing too hard to transform the physical aspects of the problem, or because you lack the skills to help transform the emotional issues in a Pleasant and Gentle and Safe fashion, or because you don't feel safe with letting her express and accept certain emotions or memories. Remember that acceptance preceedes change.
But if you can both give it a good try. She because she wants to, and you with good reason to believe that you can help her with the myriad issues usually involved in a complex life disorder like MS, then it might work very well. Or, alternately, if you and she both have a goal to just try to relieve her distress to a certain acceptable degree, "taking the edge off", and you are both comfortable with your ability to do this, then I could imagine that you would both be very happy with the results. (unless you have a fear of success, in which case you'll have to work on that too!)
I thought I'll just mention that the other 'type' of negative beliefs that are so prevalent are intergenerational ones, in which the person has 'inherited' cultural ideas which are so much a part of their lives that they don't know to challenge them. I wonder how much these play a part in 'genetic' illnesses. So you have to be a detective to find and deal with this sort of negative beliefs without getting 'infected' by them. There's also thought patterns like "depression is a good way of avoiding things" which can be very tricky to handle. But if you are OK with steering clear of these issues, and only deal with what you understand and are comfortable with, you can definitely get her to a new level of comfort. Don't be scared to say "I don't know about that". None of us have experience in everything, and it's OK to be able to help in certain areas, but not in others.
I hope that this helps!
Rachel