Assalaamu alaikum,
(smile) The problem is more the removing of the eyebrows in the first place, and then penciling in eyebrows, for beautification purposes (see the hadith below). I have read that this was a practice of the prostitutes in the Prophet's (SAWS) time.
If a women loses her eyebrows because of chemotherapy (for instance), I don't think it would be problematic for her to pencil them back in, in order to regain the use of her eyebrows (we use them while communicating, as well as they look usual).
(smile) At least, this is my understanding. But really, only Allah truly Knows.
I hope this helps.
May Allah, the Fashioner of Forms, Help us to be grateful for the forms He has Gifted us with.
Ibn Mas'ud (May Allah be pleased with him) said:
Allah has cursed those women who practise tattooing and those women who have themselves tattooed, and those women who get their hair removed from their eyebrows and faces (except the beard and the mustache), and those who make artificial spaces between their teeth for beauty, whereby they change Allah's creation. A woman started to argue with him, saying: "What is all this?" He replied: "Why should I not curse those whom the Messenger of Allah (ﷺ) cursed and who are cursed in Allah's Book? Allah, the Exalted, has said in His Book:
"And whatsoever the Messenger (Muhammad (ﷺ)) gives you, take it; and whatsoever he forbids you, abstain (from it)." (59:7)
[Al-Bukhari and Muslim].
وعن ابن مسعود رضي الله عنه قال: لعن الله الواشمات والمستوشمات والمتنمصات والمتفلجات بالحسن، المغيرات خلق الله! فقالت له امرأة في ذلك فقال: وما لي لا ألعن من لعنه رسول الله صلى الله عليه وسلم وهو في كتاب الله؟! قال الله تعالى: {وما آتاكم الرسول فخذوه وما نهاكم عنه فانتهوا} ((الحشر:7)).((متفق عليه)).
[TABLE="class: hadith_reference"]
[TR]
[TD]Sunnah.com reference[/TD]
[TD] : Book 18, Hadith 135[/TD]
[/TR]
[TR]
[TD]Arabic/English book reference[/TD]
[TD] : Book 18, Hadith 1645[/TD]
[/TR]
[/TABLE]