What do you think about me telling my heavily pregnant former co-worker she is massive?
Why do you feel the need to point that out?
She wears tight shoes that doesn't fit her.
Her shoes being too tight and telling her she is massive are two completely different things. You can offer her new roomier shoes, but telling her that she is huge is super offensive.
I've seen her eating my food the other day and she is massive.
It's normal for pregnant woman to gain weight. However, pointing this out is rude and cruel. It's best to avoid saying anything if it does not affect you.