Former manager Jonas Eidevall resigned in October, just days after the defeat at Bayern was made worse with a loss at home to WSL rivals Chelsea.
Confidence was low, results were disappointing and criticism was high.
In came Slegers, who was assistant manager under Eidevall, and the Dutchwoman instantly steadied the ship with a 4-1 victory over Valerenga.
Three European wins later, Arsenal have qualified with two group games to spare, joining Chelsea and Manchester City in the last eight.
"It's surreal to be honest. I never felt we would get into this situation," Slegers said on Thursday night.
"We have done really well but I was part of Jonas' staff and there was so much that was built during his time. I don't want to separate that."
Arsenal's quality was never in doubt. Under Eidevall they reached the Women's Champions League semi-finals in 2023 - but struggled for consistency.
Ex-Arsenal defender Anita Asante, who won the European Cup in 2007, told BBC Radio 5 Live that the players "look reinvigorated" under Slegers.
"They have a DNA. The way they are playing at the moment, everybody is just firing on all cylinders. The players look and sound reinvigorated," added Asante.
Before hosting Juventus, defender Emily Fox said the team are "very confident" and "feel together" after their recent run of form.
"Renee brings a lot of confidence, is very even-keeled and is just straightforward. I think with that, you have clarity and also freedom," added Fox.
It is clear Slegers has the players' support, with forward Beth Mead also stating she has been a "breath of fresh air" earlier this month.