I think if the rash disappears when you press on it (like if you press a clear glass onto her skin, or run your finger firmly over her skin) then it isn't too much to worry about... Where is the rash? Has it been warm where you are? It could be heat rash, and most likely is if the weather has been warm, and if the rash disappears momentarily when you press it (there is a more technical term but I can't remember it..lol).
If it's been nearly 2 weeks since her needles though it is probably fairly unlikely that they caused the rash, although with the MMR I think the side effects can be a bit delayed.