What have you been feeding her both in the soil and as watered? Too much Calcium or Potassium can lock out micronutrients like manganese. It causes burn spot that looks like this.
Please check also if pH is high. High pH is an indicator of too much calcium.
After correction, new leaves would be healthier. It is difficult for micro-elements to move up from plant root to existing growth. So, correction will work only on new growth. Spraying micro-element on leaves helps a little.