I think Isla will withdraw into herself and become introverted, She as been the precious baby of the family for seven years even isabell talks to her like she is a two year old and Isla plays that role wonderfully even openly regressing into baby toddler behaviour to make sure she is the centre of attention, They have done her no favours at all, I feel she will be deeply hurt at losing her baby role and be overwhelmed with feelings of insecurity and to hide this because she will know at the age of seven this is undesirable I think she will withdraw and be quiet and uninterested, I will be surprised if at seven years old she shows open jealousy she will find more subtle ways of showing her discomfort with the situation!