As with so many moral judgments imposed on women, it's rarely a case that some particular action or state is praised or blamed in abasolute terms, but rather that it is conditionally praiseworthy depending on how it upholds patriarchal ideals and structures. Being/remaining single may default to being discourged, but circumstances may elevate it in support of some other ideal or principle. Thus, the "widow faithful to her dead husband" is praiseworthy...unless she has failed in the higher principle of procreation. The Amazonian virgin may be very conditionally praiseworthy as a pseudo-man, but face narrative punishment for daring to step outside approved female roles.
Even when the rise of Christianity created a new context in which singlehood was praiseworthy, it was still conditional on fulfilling the requirements of the chaste religious devotee. But to judge these societies for not offering a context in which women might choose to be single (or at least, unmarried to men) for individualistic purposes is still based on culturally determined "allowable ideals" -- it's just that one of those ideals is individualism. This can be very difficult to portray in historic fiction -- and especially in historic romance, in which historic realities are more often bent to accommodate reader desires and expectations. Would your fictional historic character consider individualism an acceptable reason for deviating from the roles and behaviors expected by her society?
One work-around for the modern author is to provide the character with an acceptable in-story justification for the circumstances and goals we want her to have. But especially in sapphic historical romance, readers have a strong desire to see characters for whom same-sex desire is, in itself, a valid justification for her life choices. Not a make-do alternative when the normative life path isn't available. We want our widowed Dido to remain unmarried because, having done her duty in her first marriage, she now chooses to follow her heart and win the affections of a Camilla who is not viewed as a virago, but as embodying one of the life paths that women are capable of choosing.
Pyy, Elina. 2019. “Tracing Roman Ideas on Female Singleness: Virgil’s Aeneid” in Sabine R. Huebner & Christian Laes (eds), The Single Life in the Roman and Later Roman World. Cambridge University Press, Cambridge. ISBN 978-1-108-47017-9
A collection of papers addressing (and definine) the state of "singleness" in the Roman Empire, both in pre-Christian and early Christian times. There is a strong focus on Egypt as well as Rome proper, as well as wider Byzantine material. Comparative material is offered from Jewish sources, as well as a small selection of studies from specific cultures of more modern date.
Pyy, Elina. “Tracing Roman Ideas on Female Singleness: Virgil’s Aeneid”
This article compares the literary figures of Dido and Camilla as commentary on Roman attitudes toward deliberate singleness in women. Very briefly, Dido begins by representing the faithful widow, resolved to remain loyal to her dead husband by never remarrying. Her subsequent relationship with Aeneas can either be seen as a betrayal of this ideal or adherence to a different ideal that a childless woman should remarry. But her unhappy end implies that the relationship with Aeneas was inadequately virtuous.
Camilla also resists marriage, but as an Amazonian warrior committed to virginity and war. She represents the “man-like” woman who rejects normative womanhood and is admirable only in a masculine framing. Her dedication to virginity, while given lip service as admirable, is seen as a waste, and the nature of her death in battle can be seen almost as a “corrective rape” motif. [Note: my label, not the author’s.]
The author suggests that hypothetical Roman ideals around female chastity were contradicted by more pragmatic attitudes idealizing procreation and motherhood.