You and your girlfriend are old enough to be married without anyone's permission. She does not need her parents permission. Why on earth would she need her parents permission to either see you or hold hands with you?
We had a couple in our congregation. They were in their 30's. She was a pioneer and he was studying (like you). They started dating. There was even a 'marking' talk from the platform about it. They were both sat in the audience while it was given. It made no difference, they carried on seeing each other. They didn't care what anyone else thought. They got married, he got baptised. They are still part of the congregation and nobody says anything anymore, they are just another couple.
Don't let anyone else push you around or make you feel bad. It's your life and her life, no one elses. Live it how you want. As adults you don't need anyone telling you how you should live it.