PA-28 flight Instructor reported that while their student was performing a solo landing, they had a bird strike on final approach. During landing, the student lost aircraft control resulting in a runway excursion.

In the morning, after discussing with my student and combing through various weather reports to make an appropriate go/no-go decision, I made the determination to send my student for a solo, takeoffs and landings, to a full stop. This was to be her second solo in a 141 program. According to the ASOS and METAR, weather conditions for the morning were appropriate to a pattern solo - (according to the ASOS - called prior to walk around) winds variable at 5 knots, 10 sm of visibility, pressure 30.09, density altitude 1,675 feet. We conducted an analysis of the aircraft's performance data, located in the "performance and limitations" section of the POH to account for the day's aircraft performance. Following that, we filled up the tanks from the local FBO, and proceeded with the aircraft walk around. There were not any items damaged on the plane prior to takeoff and the aircraft was not due for any maintenance. After that, my student entered the aircraft, and departed for her second solo. After her runup was complete at the runup area, I watched her taxi for the first circuit in the pattern of the day. She was cleared for takeoff, and proceeded to takeoff and make left closed traffic. I was monitoring her progress on foreflight, and listening to her radio calls on the tower frequency. After being cleared to land, she appeared stabilized throughout her descent both on flightaware (ADS-B), and visually, and made her first of 4 landings. She adhered to my instructions, decelerating to a full stop before taxiing back to the runway for full length departures. Her second takeoff was also very stable, and once again commenced left closed traffic. On the second circuit in the pattern, she was extended downwind before being cleared for another full stop landing. While she was outside of my direct sightline at this time, in reviewing the ADS-B data, she appears to have initiated a stabilized descent at airspeeds consistent with her training. About 50 feet over the runway and prior to touchdown, my student states she "hit something and there was a loud thud on the right side of the plane." Upon debrief, she states that she believes it was a bird or possible drone strike. In the moments following the strike, she says was unfocused and continued with her landing instead of proceeding with a go-around procedure. While attempting to regain control, she suffered from a runway excursion, and hit a Runway Distance Remaining sign while departing the runway. The tower sent assistance, and she was able to get out of the grass and taxi back to the ramp under her own power. Upon post flight walk around, there was substantial damage to the aircraft's left wing, and what appeared to be an impact point of the bird strike on the right side of the cowling. According to her training, she has logged countless takeoffs, landings, and go-arounds - consistently demonstrating premier procedural knowledge of traffic pattern operations, and radio communications. During her pre-landing brief, she states to expect the go-around and has previously demonstrated that she will not hesitate to increase the aircraft's power, and initiate a go-around. My analysis is that while she was stabilized on her final descent, the strike and resulting loud thud redirected her attention and caused her to lose focus during the most critical phase of flight. Following this accident, we will be conducting 3 lessons exclusively working on go-arounds, and go- around procedures to ensure this does not happen again. During those lessons, I plan to use all the tools at my disposal to continue simulating real world distractions.