Marriage of a widow is never prescribed in Hindu scriptures. That's what Manu Smriti states.
But there is a provision for a widow without a son to procreate one with the help of her brother-in-law.
Alternatively, the widow may seek to procure a son. 23When her brother-in-law is alive, a son born to such a widow by another
person does not share in the inheritance.
Gautama Smriti 28.22-23
When her husband dies, a wife should abstain from honey, meat, liquor,
and salt, and sleep on the floor for one year; 8 for six months,
according to Maudgalya. 9
After that time, if she has no son, she may
bear one through a brother-in-law with the consent of her elders.
10Now, they also quote: One should not enjoin a leviratic union on a
woman who is barren, who has borne a son or reached menopause, whose
children have died, or who is unwilling––that is, a woman from whom a
fruitful outcome cannot be expected.
Baudhayana Dharma Sutras 2.4.7-10
Manu Smriti also states the same thing in this regard.
9.58. An elder (brother) who approaches the wife of the younger, and a younger (brother who approaches) the wife of the elder, except in
times of misfortune, both become outcasts, even though (they were
9.59. On failure of issue (by her husband) a woman who has been authorised, may obtain, (in the) proper (manner prescribed), the
desired offspring by (cohabitation with) a brother-in-law or (with
some other) Sapinda (of the husband).
He (who is) appointed to (cohabit with) the widow shall (approach her)
at night anointed with clarified butter and silent,
(and) beget one son, by no means a second.
So, it is like the Niyoga Pratha, the verse 9.60 clearly rules out the possibility of marriage and which is more explicitly ruled out in one of the verse given below:
Manu Smriti 9.64. By twice-born men a widow must not be appointed to
(cohabit with) any other (than her husband); for they who appoint
(her) to another (man), will violate the eternal law.
9.65. In the sacred texts which refer to marriage the appointment (of widows) is nowhere mentioned, nor is the re-marriage of widows
prescribed in the rules concerning marriage.