。
She's married to an English teacher, so she gets to take lessons for free.
Literal
She [topic-は] English [genitive-の] teacher [with-と] is-married [because-ので] free [with-で] lesson [object-を] can-receive [explanatory-のです].
結婚している takes the resulting-state reading: 結婚する is a change-of-state verb ('to marry/wed'), and ~ている marks the post-change state of being married. The connector ので gives a softer, more matter-of-fact reason than から ('because'). 受けらる at the end is a small writing slip — the standard potential of 受ける is 受けられる, with the ら-drop variant 受けれる widely used in casual speech as ら抜き言葉. The form here drops the れ instead of ら, which is non-standard either way; treat it as a typo and read it as 受けられる. The と after 先生 marks the marriage partner — Japanese marries 'with' someone, not 'to' them. の at the end of のです (here のだ-explanatory-のです) provides the 'here's the reason / here's the situation' frame.