Something must have
took place that created that trigger. Either you subconsciously did
something you didn't knew and it was misread from her point of view
(probably reinforced by comments and statements) or the surrounding
event add pressure onto her view about the friendship between you
and her.
This can be anything fromn innocent 'hint hint' from friends about
your intention and ideas to no-prove claims, disturbing cum suaning
from them. Chances are, you ain't at the scene to witness or defend
yourself. 
Regardless of what your intention really are, it is obvious that
she doesn't have BGR liking for you OR in some rare cases she has
(reserve psychological acts). Unless more information is feed
through your post, my stand is no for the latter possibility.
Advice?
To maintain the friendship, you have to recognise the 3 factors
land mine, personal space and innocent jokes - which will affect
the trigger, around your environment.
Land mine - Watch your own body language especially and avoid
throwing extra care and concern, even if you feel that this is what
you could do for a good friend (Key point: your preception of good
friend to her doesn't mean she feel that same way as well). Once
you across the land mine, you activate the trigger.
Innocent Jokes- Ask people around to stop disturbing as it is
affecting her. Be serious to them and seek their understanding. I
am sure they will understand (generally).
Personal space - depending on their personality, do not invade
personal space. This is highly related to land mine. Personal space
refers to the maximum behavior you can react in her presence.
Probably a friendly arm around her, xianing talks can cease if it
is within her PS.
Trigger - the result of her behavior according to the three factors
above. Likelihood is negative is the above is negative.
The sum up - be
yourself and don't feel that it is a problem because if you do
create a scene or talks things out, firstly she will feel that
there is nothing to talk about (there isn't a problem, its your
thinking and feel that makes yourself comfortable, but doesn't mean
she is the same). Secondly, you will be fuifilling her
misconception about your relationship with her. Just treat it as
normal and be generous about it. Smile and act normally. Laugh and
talk as usual. Gradually, she will return to normal as long as the
three factors above returns to positive.
Cheers
