All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
The author of 'al-Talkhees' reported in his book from Ibn Umar that the Prophet said: “A woman in her pregnancy to the time of weaning has the reward similar to the reward of the one who struggles in the way of Allah (i.e. guarding the front stations). If she dies during this time she will get the reward of martyr” . He said: al-Daruqutni reported it in his book "al-Ilal".
Imam Ibn Al-Jawzi narrated the same Hadith in his book 'Ahkam al-Nisa' (rulings of women). The researcher of this book reported from al-Azani that the chain of this Hadith is good.
No doubt, if the Hadith is correct then it proves an excellent virtue of such a woman.
However, we do not know anyone who said that all sins of such a woman would be forgiven.
Allah knows best.