You can bring up to 100 ml in a 100 ml bottle as part of your carry on luggage, so your 50 ml is within the limits as long as the bottle is no bigger than 100 ml.
(And you can take as many of those as fit in one bag, which you can seal, of one liter.)
Some airports have the bags available for free, some sell them for more than you pay for a box of bags in a supermarket.
I have at times used a smaller bag if I had only one item and if you only have one small item they may even accept a bigger bag. If you have any bag at home that might work and no time to go to a shop where they sell them, use that bag and replace it at the airport if they have better (size) ones there.
One liter bags are about the size of sandwich bags, in case you do not have a box with the size on.
Freezing is a bad plan for several reasons.
Security has been stopping people bringing frozen liquids onto planes, saying that it was still liquid. (This is not always the case but it has happened.)
The oil may not freeze, as all oils have their own freezing points.
And you can damage the goodness of the oil when you freeze it. Most medical oils have to be kept between given temperatures to stay best.
Traveling between Germany and Austria makes it very unlikely that you will run into trouble with customs, but if you feel the need you can go to the red 'something to declare' exit of the airport and ask.