Those very agents of hers were non-mahram - case in point, her trusted employee Maisara, who was the one who reported to her about the admirable character of young Muhammad (sallAllahu 'alayhi wa sallam).
As well, a false dichotomy is erected when it's implied that she didn't deal with 'strange men' - the default in Islam is that unnecessary mixed gender interaction, and inappropriate gender interaction, is what's forbidden... not respectful, dignified interaction with a necessary purpose.
The books of fiqh explicitly discuss the permissibility of women engaging in business, and in fact mention the case of a woman temporarily removing her niqab to confirm her identity for the purposes of confirming her business transaction.
For those who wish to know of other Sahabiyaat and women of the Tabi'een who had careers, Zaynab bint Jahsh was a skilled craftswoman and would make and sell her products, then give the proceeds to Sadaqah.
Samraa' bint Nuhayk wasn't a businesswoman per se, but was appointed by RasulAllah (sallAllahu 'alayhi wa sallam) to monitor the marketplaces and discipline those who were caught cheating or engaging in dodgy transactions.
Rufaydah al-Aslamiyyah was a doctor whose 'hospital' was a tent erected within Masjid an-Nabawi itself. RasulAllah (sallAllahu 'alayhi wa sallam) would send all those who were ill or wounded to her.
Hafsah bint 'Umar and ash-Shifa bint Abdullah were teachers, who taught others how to read and write.
It is said that Sawdah bint Zam'ah owned and ran a leather tanning business, and that other Sahabiyyaat such as Khawlah, Bint Fakhriyyah and others were professional traders in the perfumes.
The women of the Ansar ran their own farms and were keen as to how the produce was collected and sold.
All of these activities were careers that had these women engaged outside of merely staying home with the husband and children - they were intelligent and they put their skills to good use.
(Source: Great Women of Islam, published by Darussalam)
In short, those who claim that there is no 'evidence' of Muslim women amongst the Sahabah and Tabi'een having 'careers' are merely revealing their own ignorance and lack of knowledge and understanding.