Halszka is the Old Polish diminutive of Halina (which itself derives from Helen) — sometimes also linked to Elizabeth. A traditional Polish feminine name.
Halszka of Ostrog (1539-1582) was the Polish princess and one of the wealthiest heiresses of the Polish-Lithuanian Commonwealth.
Halszka 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 Halszka reduce to 6, The Nurturer. This is a traditional interpretive system, not a factual claim about the name.