I am sure Bindi is very adorable.
However some people just do not understand how dangerous it is to feed a Yorkie Junk. It can lead to serious, life threatning conditions .If talking to the lady does not work, then when you take Bindi to her next vet. appointment, take the lady with you. Have the vet talk to her.
Bindi's health needs to come first. In my opinion , when she gives Bindi junk food it is direspecting you and Bindi.
You have to talk to her or DB .AND enforce the issue. DO not let her keep doing this to Bindi.
You mentioned that when you Leave Bindi at home she asks about her, BUT I still think it is highly approiate to do that. For Bindi's saftey and health .LEt the lady know, honestly Bindi gets very sick after she has been to your house and she could die because she is given people food too much.
HUn, You have every right to put your foot down and not tolerate anybody who is not respecting Bindi's health and your concerns.