Is it permissible for her to pray in front of employees at work?
It is clear from your question that you work in a place where there is mixing with men. Mixing leads to many evils and things that are forbidden, as is clear to anyone who has insight. Please see question no. 1200 for the evidence that mixing is haraam.
Trustworthy scholars have issued fatwas ruling that it is haraam to work in mixed environments, such as the statement in Fataawa al-Lajnah al-Daa’imah (12/156): Mixing between men and women in schools and elsewhere is a great evil which has a serious impact on one's religious commitment and worldly interests. It is not permissible for a woman to study or work in a place where there is mixing between men and women, and it is not permissible for her guardian to give her permission to do that. End quote.
Please see question no. 6666: Should she carry on working in a job where she mixes with men?
For a woman who is faced with this problem of working in a mixed environment, if she can pray in her house, that is better, such as if she can go back home long enough before ‘Asr that she can perform Zuhr prayer. The Prophet (peace and blessings of Allaah be upon him) said: “A woman’s prayer in her house is better than her prayer in her courtyard, and her prayer in her chamber is better than her prayer in her house.” Narrated by Abu Dawood, 570; classed as saheeh by al-Albaani in Saheeh Abi Dawood. That is because it is more concealing and protects her from the gaze of men.
If she does not have time to offer the prayer in her house, then she should choose the most concealed place in her workplace, and offer her prayer there, wearing full hijab and covering all of her body. It is not permissible for her to delay her prayer until the time for it is over. Allaah, may He be exalted, says:
“Verily, As‑Salaah (the prayer) is enjoined on the believers at fixed hours”
Al-Sa’di (may Allaah have mercy on him) said:
i.e., it is enjoined at the proper time. This indicates that it is obligatory and that it has its own time, and it is not valid unless done at that time. These are the times agreed upon by the Muslims, young and old, knowledgeable and ignorant. They learned that from their Prophet Muhammad (peace and blessings of Allaah be upon him), who said: “Pray as you have seen me praying.” End quote.
Tafseer al-Sa’di, 17/255
The free woman is ‘awrah and it is haraam for her to uncover her face and hands in the presence of non-mahram men, whether she is praying or in the state of ihraam or in any other normal situation, because of the report narrated by ‘Aa’ishah (may Allaah be pleased with her) who said: The riders used to pass by us when we were with the Messenger of Allaah (peace and blessings of Allaah be upon him) in ihraam. When they drew level with us, one of us would lower her jilbaab from her head over her face, and when they had passed by us, we would uncover it. Narrated by Ahmad, Abu Dawood and Ibn Maajah. If this was done in the case of ihraam when a woman is required to uncover her face, then it is more important in other cases, because of the general meaning of the verse in which Allaah, may He be exalted, says:
“And when you ask (his wives) for anything you want, ask them from behind a screen, that is purer for your hearts and for their hearts”
It should be noted that whoever gives up something for the sake of Allaah, Allaah will compensate him with something better than it, and whosoever fears Allaah and keeps his duty to Him, He will make a way for him to get out (from every difficulty) And He will provide him from (sources) he never could imagine (cf. al-Talaaq 65:2-3). So hasten to give up working in a mixed environment, and look for permissible work that Allaah will bless.
May Allaah help us and you to obey Him and do that which pleases Him.
And Allaah knows best.