Your girlfriend is full of sheeite.
About 12 years ago my girl's team wanted to try spankies. They ordered them and were reluctant to wear them- so the came up with an idea- we went to the track and were the only ones there. They ran a lap and if they felt comfortable left school grounds and ran a 1 mile loop.
When they came back 100% said they were very comfortable.
From then on we gave the girls 3 bottoms and they could wear whichever one they wanted.
Most chose spankies, some chose one of the other two.
The girls made sure that everyone felt comfortable with their choice- no peer pressure.
Your girlfriend is likely lying to you because she doesn't want you to know that she likes the extra attention or maybe she really doesn't look good in them and is "pressured" into wearing them so she isn't seen as different.
Tell her it's ok that other guys are looking at her, she's your girlfriend, they can look and not touch.
Or, assure her that she looks great.