It doesn't sound like mastitis to me. Some blood in the milk is quite normal, especially if she also suckles a kid - his/her butting may well cause some blood vessels to rupture. One other sign of mastitis would be if her milk yield is decreasing. Also when you put the milk through a filter if she has mastitis you will feel it slowing down as it goes through the filter. It is difficult to explain, but once you have seen it you know, it is often the first sign that something is wrong. Even when they have sub-clinical mastitis they don't like you milking out the effected side, it definitely feels hotter and often has lumps in it.
I have had small(tiny) blood specks on occasion, it is known as "pink" milk.
The first choice for mastitis AB's would be Pen & Strep, not sure about the dose though from memory.