I'm not really into this kind of 'forced' concept in fanfiction. However, if we analyze it in a general sense, it might be a very dark and unethical take on the relationship between Lucy and the celestial spirits. It goes against the normal friendly or contractual relationships depicted in the original work.
Most likely not. The fan community generally values positive and respectful interpretations of characters and their relationships. A 'forced' relationship as described in this fanfiction goes against those values.
In Fairy Tail celestial spirits fanfiction, writers get creative with the powers and personalities of the spirits. Some may give a spirit a backstory that wasn't explored in the original. For instance, Aquarius could have a past that involves an ancient water civilization, which adds more depth to her character and her relationship with Lucy.
Another good one is 'Celestial Bonds Renewed'. This fanfiction explores the idea of the celestial spirits' bonds with their summoners being tested in new and unexpected ways. It's full of emotional moments between the characters, especially Lucy and her spirits.
She might start to blush furiously. Given her character, she is a bit shy when it comes to romantic matters. And then she might start to stammer out a response, not really sure what to say at first. As she composes herself, she could tell Natsu that she has feelings for him too but in a very gentle and sincere way.
One interesting aspect could be how she trains to become a Celestial Dragon Slayer. Maybe she discovers an ancient magic that combines the two, and she has to learn to control the newfound power. This could lead to some great character development as she struggles with the increased power and the responsibility that comes with it.
One possible storyline could be Lucy's adventures with her spirits as they face a powerful new enemy together. The spirits might use their unique abilities to protect Lucy.
Lucy might be heartbroken. After all, Team Natsu was like a family to her. She could initially go into a state of shock and disbelief. Maybe she would try to plead with the team to let her back in, explaining that whatever they thought she did was a misunderstanding.