When the athletic, tenacious 5-foot-8 junior guard isn't on the floor, her absence is felt, as was the case last week when a left ankle injury sidelined her for A-C's lopsided first-round Lancaster-Lebanon League playoff loss to Manheim Township.
A big difference.
On the strength of Siebecker's team-high 13 points, energetic play at both ends of the floor and, most importantly, a pressure-packed tiebreaking free throw with 5.1 seconds remaining, A-C pulled out an ugly yet beautiful 34-33 victory in front of the home folks at Annville-Cleona High School.
Now 15-9 and bound for Monday's semifinal round at Penn Manor (6 p.m. tip) against top-seeded powerhouse York Catholic, A-C hardly seemed to be on the verge of a thrilling postseason victory for much of the night.
It fell behind 9-0 quickly, managed just four third-quarter points and nearly completely gave away a three-point lead in the final 1:50 before prevailing via Siebecker's free-throw heroics.
"I was really nervous," Siebecker said with a smile of being at the line with the outcome hanging in the balance. "Because I tend to not make my foul shots too much. I was just hoping I'd get it. I took my time and worked on my form.
"It's really great because we've never gone this far, so we're happy about that."
"She's such a great outside shooter, and just athletic getting to the basket," head coach Jaime Walborn said of Siebecker's value to A-C, which now gets two cracks at securing a state playoff berth. "She makes a big difference. We missed her in the Township game, not that it probably would have made much of a difference, but we missed her. She played well tonight."
A-C also got a big effort from junior point guard Kayla Parks, who dropped in seven of her 11 points in the first half to help A-C recover from that early 9-0 deficit, as well as some needed spark off the bench from freshman guard Meredith Bachman and important senior leadership from forward Elaina Wanamaker.
It was a good thing, too, since A-C was killed in the rebounding department, where Camp Hill forwards Kierra Mitchell (14 points) and Leah Springer (10 points) feasted on second-chance opportunities.
It also struggled to develop any kind of offensive flow throughout, either missing easy shots or throwing the ball away far too much.
And it did not handle the final two minutes - when it could have put the game away in less stressful fashion - very well at all.
But it didn't shrink from the challenge for a second, either.
"There were some games this year where we just folded," Walborn admitted. "We could see that we were getting there, but we just couldn't get over that hump. This was a good game. I said to them (before the game), 'It's one-and-done. There's no room for mental lapses. You just have to stick with it.' And I thought they did."
A-C first displayed its poise after Mitchell scored the game's first seven points to spark the Lions (13-9) to the 9-0 lead midway through the first.
Parks finally got the home team on the board with a three-point play at the 4:13 mark of the opening quarter, and by the end of the first A-C was in the hunt, down 13-9.
The Little Dutchmen then took their first lead at 14-13 on a Barb Inman jumper with 4:48 left in the half and ultimately headed into the break up 20-19.
But any momentum that A-C had built in the second quarter almost entirely disappeared in a nightmarish four-point third quarter.
Fortunately for Siebecker and company, Camp Hill wasn't exactly setting the world on fire, either.
But it did pull ahead 25-24 after three quarters and nudged ahead 27-24 on a Springer jumper with 7:05 left in the game.
Meanwhile, A-C was working on a scoring drought of over six minutes and in danger of fading from the fight until Siebecker buried a corner "3" and a foul-line jumper in the span of 35 seconds midway through the fourth to give her team the lead again, at 29-27.
"There was definitely an energy shift," Siebecker said. "After making that, I even felt more uplifted. And you could just see everybody get excited that we were still in it. But everybody did it, hit key shots that helped us get pumped up and keep going."
That excitement became a 31-27 lead on a Wanamaker drive with 4:08 left, and the lead was still 33-30 after Bachman slipped in a drive with 1:50 to go.
However, A-C didn't handle itself very well from there, and overtime appeared imminent after Springer came up with a steal and set up Addison Guyer for the tying layup with 20 seconds left.
But A-C had the final say, and Siebecker uttered the final statement, finding an opening on the baseline off an inbounds play and drawing the fateful foul with 5.1 ticks left.
Her first free throw toss hit nothing but net. Her second was off the mark, and the Lions rebounded but were unable to get off a shot before time expired.
"This is what we work for," Walborn said. "We're making leaps and bounds for the program as a whole. Most of these kids have been starting since they were freshmen, so this is the time as juniors and seniors that you want to do this. We're making those strides."