blood pressure tablets

Hi all,
My lovely sis is using this website and started off slowly but surely, but after about 6 weeks, she stopped losing weight
and for the past 4 weeks has lost nothing. Now I know what she eats like and she is being totally honest that she is logging
everything that passes her lips. She's at her wits end, having ALWAYS found it very difficult to lose weight in the past. She is
quite 'puffy' (sorry sis!) so I think she is retaining water. She has high blood pressure and is on medication - has anybody had
problems with weight loss because of medication before?
By the way, she does low impact aerobics EVERY day too and is in her 50's (sorry again sis!!)
CAN ANYONE PLEASE HELP! I really feel for her!
Thanks guys