Was it customary for there to be an annual lamentation for someone's death, e.g. the daughter of Jephthah? Details as to her mourning process?

Question

In Judges 11, the overzealous (or prideful) short-reigned judge of Israel, Jephthah, makes the rash vow to G-d that if he is victorious against the Ammorites and safely returns home, then he will sacrifice the first thing he sees in the doorway in Judges 11:30-31:

And Jephthah vowed a vow unto the LORD, and said: 'If Thou wilt indeed deliver the children of Ammon into my hand, 31 then it shall be, that whatsoever cometh forth of the doors of my house to meet me, when I return in peace from the children of Ammon, it shall be the LORD'S, and I will offer it up for a burnt-offering.'

Unfortunately, that "whatsoever" is "whomever" because his daughter is the first that comes forth to meet him. (You can almost imagine an excited, eager girl anxiously waiting her father's return, running to embrace him). Sad, indeed.

Now there is somewhat a debate of whether he carried out this vow, but I think the general consensus is that he did in order to stay true to his vow (and his daughter did so knowingly and willingly). Rashi, quoting from the Medrash Rabbah, denotes a graphic scene wherein Jephthah was inflicted with a deadly diseases that deteriorated all his limbs until they became detached (as punishment for not consulting with the high priest to annul this thoughtless vow). But this isn't the thrust of my question.

Anyway, as we continue reading, his daughter is unbelievably obedient. Judges 11:37-40 describes:

37 And she said unto her father: 'Let this thing be done for me: let me alone two months, that I may depart and go down upon the mountains, and bewail my virginity, I and my companions.' 38 And he said: 'Go.' And he sent her away for two months; and she departed, she and her companions, and bewailed her virginity upon the mountains. 39 And it came to pass at the end of two months, that she returned unto her father, who did with her according to his vow which he had vowed; and she had not known man. And it was a custom in Israel, that the daughters of Israel went yearly to lament the daughter of Jephthah the Gileadite four days in a year.

Now in regards to my questions:

1. Anyone can understand why she would need a moment to "compose" (definitely an understatement) herself, and needing a few days to living out her last few days. But why two months? Is that arbitrary or was that a customary mourning period?
2. I can certainly understand why she would want to say her final goodbyes to her friends, but was it customary for women to mourn their virginity before they lost their virginity? Like before they got married? Also, she wasn't losing her virginity... but she was going to be sacrificed Clarification?
3. Why the mountains? I'm assuming: a) practicality -- it's nearby; b) remoteness -- it gives an atmosphere to contemplate/reflect/mourn; c) sacred ground -- mountains often were a place to communicate with G-d. Do you think any of these were the reasons?
4. Why did this become an annual event for the local Gilead young women? What did they do exactly? Do we know how long this continued? Do we have any evidence of this event?

I recognize that most of these answers are lost to history, but just in case, I thought I'd throw it out there, and if there are any rabbinical/scholarly commentary that address any of these questions.

Answer 1

I believe answers your questions are all found in the Metzudos David.

The first thing to note is that based on the explanation of the the commentary. It is to be noted that he is of the opinion that Jepthah did not bring his daughter as an offering in the traditional sense and rather is of the opinion that he did not allow her to be married to another man ([as implied in the Metzudos' commentary on verse 39).

[Please excuse the answers being out of order. Text courtesy of Sefaria]

Answer 2.

The Metzudos David comments on verse 37:

ואבכה על בתולי . רצה לומר , על שלא תנשא לאיש ותשאר בתולה -כי הבכיה מועלת להפיג הצער

"And I will cry over my virginity": Meaning because she will not marry a man she will remain a virgin. (For crying helps console the suffering [of her knowing that she will remain unmarried forever]

Answer for 1 and 3

The Metzudos David comments earlier on verse 37

וירדתי . כי מקום יפתח היה בהר הגבוה שבהרים אשר סביב , ולזה אמרה 'וירדתי על ההרים' , ולפי שהנדר היה להפרישה מבני אדם , ושתתבודד בעבודת ה' וכאשר עשה לה , לזה שאלה שעוד שני חדשים תלך לנפשה להשביע עינה , עד לא תתבודד :

"And I will descend [to the mountains]": Because the place of Jepthah was on the highest mountain amongst the mountains which were around [Jepthah's home] and because of that she said "...and I will descend to the mountains" and because the oath [that was made about her] was uttered from man [i.e. Jepthah] and that she be isolated with the service of G-d because and because of what was done [i.e. Jepthah's oath] to her; Thusly she asked for another two months and satisfy her suffering while she was not isolated

Answer 4

The Metzudos comments on why it was the practice.

לתנות . לדבר על לבה , להפיג צערה ולשמחה

"To lament": To speak to her heart so as to console her and make her happy

My comment: This means, according to the Metzudos that the custom was such so long as she was alive (and remaining unmarried).

Also. I highly recommend going through Tanach with the standard commentaries in the Mikraos Gedolos Chumash/Nach to have a meaningful understanding of the material discussed.

Hope this helps