The Douay is a translation of the Latin Vulgate. There are no pronouns in Latin, so when translating to English, the translator makes up whatever he thinks fits the context. However, while it works either way, I think “he” is more theologically accurate.
The Vulgate is a translation of Hebrew. FWIW, no pronouns in Hebrew either.
As nobody has yet replied to this:
The Latin says here: “
Ipsa conteret caput tuum, et tu insidiaberis calcaneo ejus.”
Ipsa is a feminine pronoun, literally translating to ‘herself’ (the masculine form is
ipse; the neuter is
ipsum).
Eius is rather ambiguous: it is the genitive singular (all genders) of the demonstrative adjective whose nominative singular form is
is (masc.)
The Hebrew runs thus: “
Hû’ yəšûfəḵā rō’š, wə’atâ təšûfennû 'āqēḇ.” Literally, it goes something like: “
Hû’ he-shall-bruise (
šûf)-you [a] head, and you (
'atâ; second person singular masculine) you-shall-bruise (
šûf)-him [a] heel.”
Hû’ is the third person singular, independent nominative pronoun. It often means ‘he’ (there was that old joke about how in Hebrew,
is who*hu’**hi’*mi 
), but apparently there are a few places in the OT where it can also mean ‘she’ - especially in the Torah.
For the most part Hebrew does not (as does English) require the use of an independent pronoun to precede a finite verb when the noun-subject is omitted. When it does appear it is usually for emphasis or in another type of construction.
One such construction is a nominal sentence or clause, that is a sentence which has no finite verb, but a noun or an adjective (including the participle as a verbal adjective) acts as the predicate. (The English must include a form of the verb “to be.” In this construction the pronoun is necessary if the noun subject is omitted: with a noun predicate, “it (is) my master” (Gen 24:65), with an adjective predicate, “he was faint” (Gen 25:29), with a participle predicate, “he (was) sitting at the door of the tent” (Gen 18:1).
When such a nominal sentence or phrase is connected with preceding material it may be translated as if the pronoun were a relative: “Bela, which is Zoar,” (Gen 14:2), “Esau, who is Edom” (Gen 36:1). Occasionally the pronoun follows the predicate: thus, “unclean it,” to be translated “it is unclean” (Num 19:15), “twenty gerahs it,” “it is twenty gerahs” (Num 18:16). This is especially true in dependent clauses such as those introduced by
ki, meaning “that,” “for,” “because”: “for unclean he,” that is “he is unclean” (Lev 13:11), “because many they (were)” (Num 22:3). This is also common with
'asher, meaning “which,” “that”: “from the beast which not clean it (is)” (Gen 7:2), “which not from your seed he (is)” (Gen 17:12), often called the resumptive pronoun.
Sometimes in a nominal sentence the pronoun stands between the subject and the nominal predicate where the English would have a form of the verb “to be”: “And Joseph, he (was) the ruler” (Gen 42:6), “you (are) he, God” (2Sa 7:28). The pronoun, which is redundant in English, is not in this case, a substitute for the verb “to be” but is used to indicate emphasis, ‘
atta hu’: It is you that. Also after an interrogative the pronoun may be added for emphasis, “who (is he that) will condemn me?” (Isa 50:9).
The pronoun may be used before a finite verb when a phrase separates the subject from the verb: “The woman whom thou gavest to be with me, she gave me” (Gen 3:12), and “one that shall come… he shall inherit (from) you” (Gen 15:4). Unless there is reason for emphasis this use is redundant in English and not generally translated.
The pronoun is also used to tie in an additional subject added after the predicate, “And Joseph returned to Egypt, he, and his brethren, and all” (Gen 50:14).
With the article, the pronoun may function as the demonstrative adjective, “that” (corresponding to
zeh “this”), “that place” (Gen 21:31), “in that day” meaning “the same day” (Gen 15:18).
hu’ may be used simply for emphasis: 'I know that he can speak" (Exo 4:14), or “the Lord, he (is) God” (Psa 100:3). The emphasis may be expressed in English by “himself,” “the Lord himself will require it” (Jos 22:23). When it is used to reinforce a preceding suffix pronoun, it is difficult to translate in writing, because the English equivalent is to put stress on that pronoun, “what he saith,” that is, what Hushai says in contrast to what Ahithophel has said (literally, “what is in his mouth,” 2Sa 17:5).
The
w and
y are not merely vowel letters as shown by the Ugaritic pronouns
huwa “he” and
hiya “she” (
hw and
hy).
Unexplained is the usage in the Pentateuch and a few other places where
hw’ means either “he” (vocalized
hu’) or “she” (vocalized with a perpetual qere
hi’). In the past this has led some to feel that the original pronoun for both genders was
hw’ but Ugaritic denies this conclusion. Apparently the situation is due to some dialect or vagary of a scribal school.
), it’s really hard to say, but I think it likely that the Bible you have is a 
