Milica (Милица) is the Serbian feminine diminutive of mil (gracious, dear). Princess Milica (1335-1405) was the Serbian queen who ruled after the death of Prince Lazar at the Battle of Kosovo.
Milica is widely used in Serbia.
Milica does not currently appear in the US Social Security Administration's top 1,000 girls' names, so we don't publish a US rank or birth count for it. That says nothing about the name's standing elsewhere in the world — only that it sits outside the ranked US data we rely on.
In Pythagorean numerology the letters of Milica reduce to 2, The Peacemaker. This is a traditional interpretive system, not a factual claim about the name.