Extensions on client with hair loss/bald patches?

I recently had a consultation with a lady that has very thin hair and some hair loss/bald patches from wearing clip ins for years. She wants some pre bonded hair extensions. I was wondering if I need or should get her to sign anything just to say the hair loss was already there before the extensions In case I do her extensions and then after she thinks there is more Hair loss or something?

I just find with some clients when I have taken out all there extensions they think there hair is...

Extensions on client with hair loss/bald patches?