I'll deal with Junia's gender first. Although the Greek manuscripts are ambiguous as to her gender, Wikipedia says "the consensus among some modern New Testament scholars is that Junia was a woman" and points out that the first known reference to Junia as a male comes from Origen no earlier than the late second century, although from a late medieval copy of Origen's writing. So it seems the Church Fathers accepted Junia to have been a woman and, given the potential for scribal bias, it is even possible that Origen had also believed this. Papyrus 46, a Greek manuscript from about 200 CE, alters the name used in Romans 16:7 from Junia to Julia, which provides some support for her to be a woman, even if this spelling is not original.
Wikipedia (ibid) cites Rena Pederson, who argues "medieval translators such as the 13th-century Archbishop Giles changed her name to Junias, as a reflection of an institutional prejudice against women that stretched back to ancient Greek scholars." Stephen Finlan also writes that "Junia is clearly a female name that was changed to the male "Junias" in the Latin translations of the New Testament."
Rena Pederson (The Lost Apostle, page 164) says multiple database searches found the female name in use in Ephesus, Didyma, Lydia, Troas, Bithynia and Rome during the first century, but not one reference to the masculine form, Junias. She says "the male name was simply not a bona fide name".
According to a Christian blog, cbmw.org, the Church Fathers not only regarded Junia to be a female, but actually identified her as the wife of Andronicus. It says "many patristic exegetes understood the second person mentioned in Rom 16:7 to be the wife of Andronicus, such as: Ambrosiaster (c. 339-97); Jerome (c. 342-420); John Chrysostom (c. 347- 407); Jerome; Theodoret of Cyrrhus (c.393-458)." The site goes on to list other exegetes holding this view, but they were too late to be regarded as Church Fathers.
The Greek is also somewhat ambiguous as to whether Junia was a prominent apostle or "well-known to the apostles". There is a tendency to limit the use of 'apostle' to the twelve disciples and Paul himself, but Paul did use the term more broadly in the context of being a 'messenger' of Christ.
If Paul did regard Junia as a church leader, she would not be alone. Paul also regarded Priscilla to be a church leader, as we see in:
Romans 16:3: Greet Priscilla and Aquila my helpers in Christ Jesus
1 Corinthians 16:19: Greet Priscilla and Aquila my helpers in Christ Jesus.
Ephesians 3:5-6, although possibly not part of a work written by Paul, implies that more apostles were appointed after the time of Christ:
Ephesians 3:5-6: Which in other ages was not made known unto the sons of men, as it is now revealed unto his holy apostles and prophets by the Spirit;
6 That the Gentiles should be fellowheirs, and of the same body, and partakers of his promise in Christ by the gospel.
Thus there is ambiguity in the text, both as to whether Junia was a woman and whether she was an apostle, but the weight of scholarly opinion is that Junia was a female apostle. The implication is that females such as Priscilla and Junia were leaders of the early church.
