How to benefit from the last 10 days of Ramadhan if you don't have to pray? A girl's guide

I often hear women complain about the time when they are menstruating "Oh, I hate not being able to pray, I had developed such a good routine and now it's all on hold."

Not being able to pray is a blessing itself. It has been written by Allah for us and there is wisdom behind it that we may or may not be able to understand.
But having your menstruation does not mean you stop being believers of God. We don't stop with Ibadah and we are not deprived of any blessings.
Don't take this as an excuse to sleep in, binge watch Netflix or waste your time in any other way.
Try to still benefit from the last 10 days of Ramadan. The days of forgiveness. Try to experience the night of Decreee (Laylat-ul-Qadr).

Here are some ways in which you can worship while menstruating.

1. Wake up at Tahajjud time...
   Even though you are not able to perform your Salah, you are still able to pray. Wake up, get out of bed, fresh up and then find a place in your home where you can dedicate time to the remembrance of Allah. Have a list of prayers written down, with translation and go through each prayer. Concentrate on its meanings and try to attain a deep heartfelt desire to be able to perform sincere prayers. Hadhrat Aisha relates that the Holy Prophet Adviced her to pray for forgiveness during the last 10 days.
   
   "Allahumma innaka 'afuwwun tuhibbul 'afwa fa'fu 'annee" (Ahmad, Ibn Majah, and Tirmidhi).
    O Allah, You are pardoning and You love to pardon, so pardon me. 
2. Prepare and eat Sehri
   The Messenger of Allaah (salallaahu ‘alaihi wa sallam) said,“Whoever feeds a fasting person will have a reward like that of the fasting person, without any reduction in his reward.”
3. Same goes for
    “Eat suhoor, for in suhoor there is blessing.” (Bukhari)
4. Give Sadaqa/Zakaat each day
   If one of the night where you give into charity falls on Laylat-ul-Qadr, it will be as if you have been giving charity for 83 years.
5. Read religious books
   Reading religious books helps you improve your Imaan. It is a way of remembering Allah, building Taqwa and increasing your knowledge. My personal favorite are:
1. Remembrance of Allah - by Hazrat Mirza Bashiruddin Mahmud Ahmad, Khalifatul Masih II(ra)
2. Our God- Hadrat Mirza Bashir Ahmad (ra)
3. Noah's Ark - Hazrat Mirza Ghulam Ahmad, (The Promised Messiah and Mahdi)
6. Watch MTA
   Try to increase your remembrance of Allah in every way possible. Just having MTA running in the back, while you go along doing your chores. You might catch yourself listening to interesting discussions or any recitation of prayers, which you know as well and can recite along.
7. Encourage your family to increase their Ibadah
   Wake your family members for Sehri and encourage even little children to pray two Raka'at and eat Sehri with you. This way you establish an importance for your family members, they understand and feel that it is Ramadhan and that this is a special time of the year.
   Even during the day time, encourage them to read more Quran, watch MTA or offer voluntary prayers, instead of letting them watch TV and be on their phones.

These are just some suggestions. There needs to be an effort, and rewards would be immense.