Qual é a diferença entre I can't help thinking of her. e I can't help missing her ?Você pode indicar exemplo de resposta.

It would be better if it's something like
'I can't stop thinking of her'.
and
'I can't stop missing her'.

If you say 'I can't stop thinking of her', it means you are thinking about her all the time and can't even stop it.
e.g. I just meet her for a minute, but I can't stop thinking of her.

If you say 'I can't stop missing her', it means You are being sad, you want her to be around you as before and can't stop that sad moment.
e.g Even though we broke up, I can't stop missing her.

( :D Honestly I would say it's a bit strange to me to share you the meaning of thnking and missing. I mean the words 'missing and thinking' are already the simple words.)