The general rule with snot and phlegm is that
If its yellow or clear it is usually a virus (ie a cold) and antibiotics will not work as they only work on bacterial infections
If its green usually it is a bacterial infection and a visit to your GP may help.
This is not 100%, but it usually the case and the more you can avoid getting antibiotics for a virus the better for your child as really you are giving them a treatment that is ineffective.

A tempreture is your bodies natural immune response to an infection, by raising the core tempreture it kills off many infections... of course you need to make sure that it doesnt get too high.

If you are concerned take her to see your Dr for piece of mind, but does sound like a cold to me... and i agree with Kimbaz, lots of rest and healthy food (and cuddles). When she is feeling better though take her out for a walk, my mum always use to say that when you are on the mend it helps blow the cobwebs away, and it always use to make us feel fresher and more clear.

HTH and i hope that Mackensie is feeling better soon