Will the questioner be sinful if she leaves the teaching profession, even though she has acquired religious knowledge, or is it incumbent upon her to combine the two, and how can she reconcile the Hadith: "Whoever conceals knowledge will be bridled with a bridle of fire on the Day of Resurrection" with the fact that she finds herself strong in the religious field?

There is no objection to teaching the English language if the work is free from intermingling and ostentation. And refraining from teaching it is not considered concealing knowledge, for what is meant by concealing knowledge is concealing Sharia (definition) knowledge when there is a need for it or when it is not available from anyone else. It is possible to combine worldly work with seeking Sharia knowledge by organizing time and perseverance, and teaching can be a means of guidance and calling to Allah. And if you are able to teach English now and enroll in a Sharia college, then transition to teaching Sharia sciences, there is much good in that.