wow..i must say, you beat alot of guys out there already, with
your courage!
good job dude! 
just reply her, the msg was meant for you! at least let her know
your intention.. she may have reject you this time, but you nv
really know the reason right?
The worst scenario is, she doesnt like you...
The middle scenario is, she just taken aback..not prepared.
the best scenario is, she is really busy that day..
out of 3, you have 2 chances of hitting the better options..try
sounding her out in your next msn chat...
good luck! 