its hard to say because our instincts are to nurture them when they need it, but in this case your sister may have reasons, such as her health, not to do it to much. She may not be physically coping with a child who constantly needs to be held. I had a friend who had a very clingy baby and he was like that up until he was about 4yrs old. She couldnt even go to the toilet without him hanging onto her so its not always something they grow out of in the first year or two....sometimes it drags on for years.

First and foremost i would want my rights to decide how to parent my kids be respected and observed. So just consider if you do go contrary to what she's asked, she may be reluctant to ask you next time. She's probably worked really hard to get him to settle without being held, so if you do start picking him up to settle, its going to be more work for her when she's out of hospital and you have to ask if she really needs that at such a time. You could ask your sister what she does in compensation of being carried around...maybe she's found something else that comforts him that he enjoys. If not, maybe you can try something different with him like a comfort teddy or pillow to hold.