A few corrections:
‘Helen is thoughtful of me….’
Depending on what you are treying to say, there are 2 different ways of correcting the second sentence:
“She bought a beautiful pair of sunglasses for me when she knew I needed them.”
(she purchased them for me)
“She brought a beautiful pair of sunglasses to me when she knew I needed them”
(she gave them to me)
instead of ‘a beautiful pair of sunglasses’, you could also use ‘some beautiful sunglasses’. Sunglasses is always plural.