My BMI was mid thirties and raised an issue. I said i would try and lose weight and I did try. It was not something they followed up. I am still, 5 years down the track) trying to lose weight!
Do you recognize why a high BMI could be a problem?
If possible do not fight them on this, there is no point. Say what they want to hear, that you are trying, whatever you are doing. If you can lose it, fab for you and for the children you will care for. Being overweight is strain.
In terms of not getting along with social worker, my honest advice is, try hard to get along with them. you could ask to change social worker but that would probably go against you. The process it relatively quick and the social worker came to visit us maybe once a week. So once a week for an hour or two we needed to speak to her and she to us and we managed fine.
Eventually, she passed us on to social worker number 2, who I did not like much, who went on sick leave quite soon and onto number 3 who was fabulous.
My advice is to stay with her/him, work with them, work on the weight and see what happens next.
Good luck.