Why does the Tie Fighter strafe Jyn when she was on the tower?

Question

In Star Wars Rogue One, during the scene at the top of the transmission tower, a random TIE (Interceptor, maybe?) from out of nowhere strafes Jyn while she is trying to align the relay rod on Scarif.

Recognizing that this may have been one of the reshoots, is there an in-canon explanation as to who authorized this or why it may have occurred? Have there been instances where pilots take it upon themselves to actively fire upon one of their own facilities without order from above for a perceived ground threat?

• Krennic was on his way up to the top of the tower and would want to avoid being shot, so he would avoid ordering a speeding vehicle with low targeting ability to strafe the tower to hit a single person.
• Central command was in disarray dealing with the incursion in space and on land
• The TIE Fighters were actively engaged to deal with the X-Wing presence

Answer 1

No, there doesn't appear to be any indication of who ordered it

This is the only thing the novelization has to say:

The shriek of a TIE fighter rose on the wind, but at first she ignored it. Then the vessel itself swept into view, descending toward the platform with its great cockpit eye fixed on her. She froze, unsure whether to run or to drop to the catwalk in the hope of hiding.

She ran, and the fighter’s cannons pulsed.

^{Rogue One: A Star Wars Story - Official Novelization Chapter 21}

As you say, it was unlikely to be Krennic. Possibly somebody in a command role noticed the dish being re-aligned and, knowing the danger of the plans being broadcast, dispatched a TIE to investigate. However, it's equally possible that the TIE pilot simply did take it upon themselves; we know from the canon novel Lost Stars that officers of a certain rank (the officer quoted below is a Commander) have the authority to make tactical decisions on-the-fly (emphasis mine):

Ciena took her TIE Interceptor up over the main bridge area of the Annihilator, just in case some rebel pilot decided to fly directly into it and go out in a blaze of glory. The other TIEs stuck rigidly to established attack patterns, but her rank gave her the freedom and responsibility to judge the battle for herself and go wherever she was needed most.

^{Lost Stars Chapter 25}

It's entirely possible that a command officer picked up Jyn's lifesign reading and went to investigate, opening fire when it became clear that she wasn't meant to be there.

Answer 2

The film's junior novelisation indicates that a sole pilot spotted her on the mast and apparently assumed that she was a rebel intent on some form of sabotage

Jyn wanted to pump her fist in triumph, but her work wasn’t done. The channel to the rebel fleet might finally be open, but she still needed to get back to the transmitter and push the button to send the plans.

At that moment, a TIE fighter pilot spotted her standing there, vulnerable and alone, and it screamed straight for her, firing its weapons the entire way. She spun about and charged back down the gantry toward the tower’s roof.

She managed to evade the TIE fighter’s strike, but the blasts tore the gantry apart. She felt herself falling and reached out to find something—anything—to keep her from toppling off the tower to the ground far below.

_{^{Rogue One: A Star Wars Story – A Junior Novel}}