The Big Bang Theory, while about geeky scientists, was also littered with various amounts of pop culture and trends. While she wasn't as academically intelligent as the likes of Sheldon and Leonard, Penny did show she had a better grasp of general knowledge as she knew a lot about the entertainment industry. She also seemed to be an avid fan of music as well, and would either be dancing or singing in her apartment to the newest hits that were soaring through the charts (so it's likely that fans would have seen her sing a few Taylor Swift songs if it had been renewed once again).
Given the chance, the writers could have potentially added even more Taylor Swift references, since Penny, Bernadette, and Amy would often be seen debating about current trends. Amy would have certainly been intrigued by the idea of the queen of pop having a song that perfectly captured her and Sheldon's relationships, and might have eventually tried to give every other pairing one. While only a few could answer this question properly, there is a possibility that the girls could have went with these choices.
Penny and Kurt
All Too Well (Taylor's Version)
Kurt was Penny's boyfriend from Nebraska. It's never made 100% clear how long the two dated, but it seems like a while. Kurt was rude, arrogant, and not a likable guy. He's the exact opposite of Leonard, and this is reinforced through his actions and how he treats Penny.
One of Swift's most popular songs, "All Too Well" sums up their relationship incredibly well - especially with lyrics like "And I know it's long gone and that magic's not here no more. And I might be okay but I'm not fine at all." The relationship left Penny feeling disoriented and confused but ultimately betrayed.
Penny and Zack
We Are Never Ever Getting Back Together (Taylor's Version)
Penny and Zack were on and off again for years. They met at Penny's work (The Cheesecake Factory), but could never quite find the right reason to make their relationship work. It all came to a head when they accidentally got married in Vegas, something that Penny later regretted.
"We Are Never Ever Getting Back Together" is the perfect song for these two. On again and off again, the relationship had taken its toll on Penny, who eventually found the whole thing exhausting because they weren't right for one another.
Leonard and Priya
Blank Space
Priya (Raj's younger sister) had no real intentions of pursuing a long-term relationship with Leonard. She tried to change him and often made fun of him for his interests and hobbies. However, Leonard was willing to do anything she asked, even moving halfway across the world for her until Penny stepped in.
"Blank Space" is exactly how Priya views Lenoard - a name to fill an empty space in her life. The lyrics "We'll take this way too far. It'll leave you breathless, or with a nasty scar," bear an uncanny resemblance to the turbulence of their relationship.
Raj and Anu
Tolerate It
Raj and Anu's relationship starts off as something that feels forced. Both of them are looking to get their parents off their backs, and finally settle down after years of luckless love.
Although the two of them grow to like each other, they still don't form that important romantic bond. "Tolerate It" speaks of a similar struggle in a relationship, especially with the lyrics "I know my love should be celebrated. But you tolerate it." Raj eventually realized that he had so much love to give, and it should be shared with someone who loves him back, not just someone who tolerates him.
Raj and Lucy
Peace
Raj and Lucy seem like a perfect match at first. With Lucy's social anxiety and Raj's struggle to speak to women, they understood each other better than anyone else. Although their interactions were a little awkward at times, they were often quite endearing and were worth rooting for. Sadly, it all became too much for Lucy.
Swift's emotional song about giving her partner peace of mind is the best reflection of this unfortunately doomed relationship. The repeated lyric "Would it be enough if I could never give you peace?" resonates with this failed relationship, Raj and Lucy could never give each other peace.
Stuart and Denise
Enchanted
For the longest time, it seemed as if Stuart would never find love. He was content with running his comic book store and the occasional hanging with the gang. But when Denise started working at the store, it was clear that the two were destined for each other.
To put it simply, the two are enchanted with each other. Swift says it best, "All I can say is, I was enchanted to meet you." They can be themselves around each other, however geeky or weird that may be.
Raj and Emily
The 1
This seemed like the one that would have worked for Raj. Emily was smart, nerdy, and had the same level of weirdness that matched Raj's. She also actively encouraged Raj's hobbies and fit into his friendship group extremely well.
However, Raj ended up cheating on Emily, ultimately ending what could have been the perfect relationship for him. It's easy to see why "The 1" is the soundtrack for their relationship - especially with lyrics like "And if my wishes came true. It would've been you. In my defense, I have none."
Leonard and Penny
Invisible String
It was love at first sight for Leonard, maybe less so for Penny. Regardless, the two of them spent the entire series having almost maybe moments, constantly circling back to each other. They were destined from the start.
This is why "Invisible String" captures the two of them so well. "And isn't it just so pretty to think, all along there was some invisible string, tying you to me?" It seems like this is the case as the two of them are like magnets, meant to find one another.
Sheldon and Amy
You Are In Love
Sheldon was perhaps the least likely to get married out of the gang. Sheldon has expressed several times his disinterest in the matter, and how he was content alone. But when Amy walked into his life, it was destiny.
They both help each other to open up and become better people as the show progresses. Sheldon often struggles to express his emotions, which is why "You Are In Love" sums up his thoughts. "One night he wakes, strange look on his face. Pauses, then says. You're my best friend." The two of them are best friends and partners all at once.
Howard and Bernadette
Lover
Howard and Bernadette are the textbook definition of a timeless relationship. The two of them dated for a while, before their eventual marriage. Despite Bernadette radiating some of the same traits as Howard's mother, it's clear that their relationship was built on mutual trust and love.
It's no surprise that "Lover" is the track for their relationship. The two of them are often the more responsible couple in the group, with them being the main couple the gang comes to for advice. Lyrics like "We could let our friends crash in the living room. This is our place, we make the call," show the beautiful simplicity of their relationship.