"We make it."
sé/sí specify who is doing the "making" when used after a verb. é/í are used to refer to objects being made (unless the copula, "is", is used). You can tell that é is appropriate here because the verb, déanaimid, has already inherently specified the "maker" as we/us. sé/sí can mean it(masc.)/it(fem.) but only when used appropriately. Example: Déanann sé cáca (It made cake).
Tangent: The general trend I have noticed is that when verbs involve me, as in the "I" and "we/us" cases, there is a specific conjugation where the "mé" or "muid/sinn" is contracted into the verb. Example: Táim, Ithim, Siúlaimid, Rithimid. For everything else, namely tú/sé/sí/sibh/siad (you(sg.)/he/she/you(pl.)/them), there is a general conjugation followed by the appropriate pronoun. Example: Tá tú/sé/sí/sibh/siad , Itheann tú/sé/sí/sibh/siad, etc...
This isn't translated as "we do it" because it's an English to Irish exercise. The reverse exercise from Déanaimid é to English can indeed be translated as either "we do it" or "we make it".
The Irish for "make" is déan.
De Bhaldraithe's Foclóir Gaeilge-Béarla has two parts to its entry for déan - the 2nd part starts with
II. Make. 1. (a) Create, construct, fashion, manufacture. An Té a rinne neamh agus talamh, He who made heaven and earth. Teach, bád, bóthar, canáil, a dhéanamh, to make a house, a boat, a road, a canal. Culaith, cathaoir, inneall, gunna, a dhéanamh, to make a suit, a chair, an engine, a gun. Éadach, im, plúr, a dhéanamh, to make cloth, butter, flour.
There is a separate entry in the FGB for déan de - "make of".