Me too but they see these type of letters day in day out.
If you are honest, provide all the correct evidence and information then you will get the visa.
A word opf advice, don't make it financial, it her letter she says you take good care of her and her family how? It has to be financial as you don't live there so I asusme you send money. Don't let the ECO think yoru relationship is about her wanting to be with you for money.