Translation:She agreed with him before I told her.
sula (sular in the past tense) is used with verbs. roimh is used with nouns and pronouns.
From the examples in the FGB entry for sula:
sula n-éiríonn siad ar maidin - "before they get up in the morning"
sula mbíonn an ghrian ina suí - "before the sun has risen"
Gach maidin sula dtéimis ar scoil - "each morning before we went to school"
sular cheannaigh mé an leabhar - "before I bought the book"
sular casadh orm é - "before I met him"
sular íoc mé as - "before I paid for it"
sula n-imí tú - "before you go"
sula mbrisfidh siad é - "before they break it"
sula dtugadh sé dom é - "before he would give it to me"
sula eclipses the following verb. sular is only used with regular past tense verbs, which are lenited, and sular doesn't make any change to that, leaving the verb lenited. The saorbhriathar is not lenited in the past tense, and it is not lenited after sular (dúnadh an doras, sular dúnadh an doras). The "past particle" do is not needed after sular, so it isn't used.