There are a few different explanations for that phrasing. In short, either a woman with long hair means a free woman and is repetitive, or the word translated as "with long hair" is mistranslated.
Firstly, the precise word in this law code translated here as "with long hair" is locbore. Locbore is a hapax legomenon, meaning it only appears once in the materials that have survived to us, so its meaning is not necessarily clear. Some scholars have chosen to translate it as "with long hair", thinking it is derived from the word locc, meaning hair--as in a "lock of hair"--and bore / bora meaning "bearer". In other compounds, locc loses the second c when a prefix, so it is reasonable that loc- is derived from locc. These scholars have then argued that a woman with long hair is a freeborn woman, and that this is a tautology. However, in Salic and Longobardic law, a "woman with long hair" is a phrase used to refer to virgins, but in Aethelbert's laws the word mægþ is used for that meaning, as in #74. As such, the scholars who support this have argued that a woman with long hair meant a free woman, as opposed to an enslaved woman, and not that it meant a virgin. However, this connection between freedom and "long hair" is not supported by any other surviving sources.
Loc- could also, however, mean a lock, as in what secures a door. Bore has the same translation from all scholars--"bearer". This is also seen in sweordbera "sword-bearer", as well as in other words. The scholar Christine Fell has persuasively (in my opinion) argued that this is the correct translation, and that locbore should be translated as "holding the keys". What does this mean? Numerous key-shaped objects known as "girdle-hangers" have been found in women's--but not men's--graves. Furthermore, these are typically not found in graves containing jewelry, indicating that they may have a connection to lower-class individuals. It is generally accepted that women had control over many areas of the domestic economy, so Fell argues that locbore is referring to that. A friwif locbore would be translated then as "free woman controlling the keys", meaning a woman in a wealthy household with great domestic responsibility, but probably not the woman of the house, so to speak.
This second explanation also makes more sense given the severity of the fine--30 shillings was significantly more than the price for breaking someone's arm (6 shillings), breaking into someone's home (also 6 shillings) and binding a freeman (20 shillings). As such, this fine makes sense to only be levied on someone with an extraordinary amount of responsibility, especially as the word for misconduct is so vague.
To summarize, there are two possible explanations for this--that the law refers to free women, and that long hair was associated with freedom, in contrast to enslaved women, who were not "long haired," or, secondly, that the law refers to one "bearing the keys", and has nothing to do with hair.
Source: A "friwif locbore" revisited, Christine Fell https://www.jstor.org/stable/44510793?seq=1