Am I sinful for conveying a fatwa to my mother permitting the removal of facial wrinkles by injection, knowing that most fatwas do not allow it, and feeling regretful?

If the website is trustworthy, then you are not at fault, because you asked the people of knowledge, which is the duty of the common person. However, if it is not trustworthy, then you have erred and you must seek forgiveness and investigate in the future. The issue of eyelash extensions is one about which contemporary scholars have differed. The preponderant view, in our opinion, is that it is prohibited if it is solely for beautification.