Re: although dirt would wash away
She started to sketch her map in the dirt but soon realised that the dirt might be washed away and therefore her map would be washed away at the same time. She also realised that if she made the map using pieces of fabric, she would be able to keep it. The fabric would not be destroyed as easily as the dirt. I agree with you that "although" was a slightly odd choice. I would simply have said "She soon realised that dirt might/would wash away but she could create a map in fabric and it would remain".
Remember - correct capitalisation, punctuation and spacing make posts much easier to read.