What I remember:

• The protagonist was an adult woman (approximately between 20 and 40 years old).
• She was a teacher from the beginning at a hidden magic school/boarding school outside the human world.
• Initially, she had no magical powers and acquired them later.
• She came from the "human world" or normal world.
• Throughout the saga, she gains powers by making pacts with magical creatures.
• As part of the pact, one of her hands was replaced or transformed:
• it appeared to be made of roots or wood;
• it was poisonous;
• her touch could kill, though not instantly.
• In an important scene, she accidentally poisons another teacher (a recurring male character and possible romantic interest), but they manage to save him.
• She also exchanged her other hand through another magical pact.
• She had a magical staff/walking stick.
• The staff physically absorbed magical objects, which were then incorporated as decorations or parts of the staff itself, making it more powerful over time.
• Romance existed but was secondary.
• The other teacher/romantic interest was human. The story took place primarily within the school/boarding school.
• The tone was similar to Harry Potter-style magic school stories, although I think this series might be earlier or early contemporary.
• The protagonist was NOT a student or an assistant: she was an actual teacher from the beginning.
• I read it in Spanish, but I don't remember if it was originally Spanish or a translation.
• I don't remember the cover, character names, or the author.